def _binopt(self, other, op):
"""apply the binary operation fn to two sparse matrices."""
other = self.__class__(other)
# e.g. csr_plus_csr, csr_minus_csr, etc.
fn = getattr(_sparsetools, self.format + op + self.format)
maxnnz = self.nnz + other.nnz
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices),
maxval=maxnnz)
indptr = np.empty(self.indptr.shape, dtype=idx_dtype)
indices = np.empty(maxnnz, dtype=idx_dtype)
bool_ops = ['_ne_', '_lt_', '_gt_', '_le_', '_ge_']
if op in bool_ops:
data = np.empty(maxnnz, dtype=np.bool_)
else:
data = np.empty(maxnnz, dtype=upcast(self.dtype, other.dtype))
fn(self.shape[0], self.shape[1],
np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype), self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype), other.data, indptr,
indices, data)
A = self.__class__((data, indices, indptr), shape=self.shape)
A.prune()
return A
def tocsr(self, copy=False):
"""
Convert this matrix to CSRSymMatrix format. Remains symmetric
Returns
-------
CSRSymMatrix
"""
from pyomo.contrib.pynumero.sparse.csr import CSRSymMatrix
if self.nnz == 0:
return CSRSymMatrix(self.shape, dtype=self.dtype)
else:
M, N = self.shape
idx_dtype = get_index_dtype((self.row, self.col),
maxval=max(self.nnz, N))
row = self.row.astype(idx_dtype, copy=False)
col = self.col.astype(idx_dtype, copy=False)
indptr = np.empty(M + 1, dtype=idx_dtype)
indices = np.empty_like(col, dtype=idx_dtype)
data = np.empty_like(self.data, dtype=upcast(self.dtype))
coo_tocsr(M, N, self.nnz, row, col, self.data, indptr, indices,
data)
x = CSRSymMatrix((data, indices, indptr), shape=self.shape)
if not self.has_canonical_format:
x.sum_duplicates()
return x
def _mul_sparse_matrix(self, other):
M, K1 = self.shape
K2, N = other.shape
major_axis = self._swap((M, N))[0]
other = self.__class__(other) # convert to this format
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices))
fn = getattr(_sparsetools, self.format + '_matmat_maxnnz')
nnz = fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype))
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices),
maxval=nnz)
indptr = np.empty(major_axis + 1, dtype=idx_dtype)
indices = np.empty(nnz, dtype=idx_dtype)
data = np.empty(nnz, dtype=upcast(self.dtype, other.dtype))
fn = getattr(_sparsetools, self.format + '_matmat')
fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype), self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype), other.data, indptr,
indices, data)
return self.__class__((data, indices, indptr), shape=(M, N))
def __add__(self, other):
# First check if argument is a scalar
if isscalarlike(other):
res_dtype = upcast_scalar(self.dtype, other)
new = dok_matrix(self.shape, dtype=res_dtype)
# Add this scalar to every element.
M, N = self.shape
for i in xrange(M):
for j in xrange(N):
aij = self.get((i, j), 0) + other
if aij != 0:
new[i, j] = aij
# new.dtype.char = self.dtype.char
elif isinstance(other, dok_matrix):
if other.shape != self.shape:
raise ValueError("matrix dimensions are not equal")
# We could alternatively set the dimensions to the largest of
# the two matrices to be summed. Would this be a good idea?
res_dtype = upcast(self.dtype, other.dtype)
new = dok_matrix(self.shape, dtype=res_dtype)
new.update(self)
for key in other.keys():
new[key] += other[key]
elif isspmatrix(other):
csc = self.tocsc()
new = csc + other
elif isdense(other):
new = self.todense() + other
else:
raise TypeError("data type not understood")
return new
def tocsc(self, copy=False):
"""
Convert this matrix to Compressed Sparse Column format
Returns
-------
CSCMatrix
"""
from pyomo.contrib.pynumero.sparse.csc import CSCMatrix
if self.nnz == 0:
return CSCMatrix(self.shape, dtype=self.dtype)
else:
M, N = self.shape
idx_dtype = get_index_dtype((self.col, self.row),
maxval=max(self.nnz, M))
row = self.row.astype(idx_dtype, copy=False)
col = self.col.astype(idx_dtype, copy=False)
indptr = np.empty(N + 1, dtype=idx_dtype)
indices = np.empty_like(row, dtype=idx_dtype)
data = np.empty_like(self.data, dtype=upcast(self.dtype))
# TODO: check why scipy does this and not coo_tocsc
coo_tocsr(N, M, self.nnz, col, row, self.data, indptr, indices,
data)
x = CSCMatrix((data, indices, indptr), shape=self.shape)
if not self.has_canonical_format:
x.sum_duplicates()
return x
def diagonal(self):
"""Returns the main diagonal of the matrix
"""
# TODO support k-th diagonal
fn = getattr(_sparsetools, self.format + "_diagonal")
y = np.empty(min(self.shape), dtype=upcast(self.dtype))
fn(self.shape[0], self.shape[1], self.indptr, self.indices, self.data, y)
return y
def _mul_multivector(self, other):
# matrix * multivector
M, N = self.shape
n_vecs = other.shape[1] # number of column vectors
result = np.zeros((M, n_vecs), dtype=upcast(self.dtype, other.dtype))
for (i, j), v in iteritems(self):
result[i, :] += v * other[j, :]
return result
def dtype(self):
"""
Returns data type of the matrix.
"""
# ToDo: decide if this is the right way of doing this
all_dtypes = [blk.dtype for blk in self._blocks[self._block_mask]]
dtype = upcast(*all_dtypes) if all_dtypes else None
return dtype
def get_projection(b, W, AW,
# TODO: AW optional, supply A
x0 = None,
inner_product = ip):
"""Get projection and appropriate initial guess for use in deflated methods.
Arguments:
W: the basis vectors used for deflation (Nxk array).
AW: A*W, where A is the operator of the linear algebraic system to be
deflated. A has to be self-adjoint w.r.t. inner_product. Do not
include the positive-definite preconditioner (argument M in MINRES)
here. Let N be the dimension of the vector space the operator is
defined on.
b: the right hand side of the linear system (array of length N).
x0: the initial guess (array of length N).
inner_product: the inner product also used for the deflated iterative
method.
Returns:
P: the projection to be used as _right_ preconditioner (e.g. Mr=P in
MINRES). The preconditioned operator A*P is self-adjoint w.r.t.
inner_product.
P(x)=x - W*inner_product(W, A*W)^{-1}*inner_product(A*W, x)
x0new: an adapted initial guess s.t. the deflated iterative solver
does not break down (in exact arithmetics).
AW: AW=A*W. This is returned in order to reduce the total number of
matrix-vector multiplications with A.
For nW = W.shape[1] = AW.shape[1] the computational cost is
cost(get_projection): 2*cost(Pfun) + (nW^2)*IP
cost(Pfun): nW*IP + (2/3)*nW^3 + nW*AXPY
"""
# --------------------------------------------------------------------------
def Pfun(x):
'''Computes x - W * E\<AW,x>.'''
return x - numpy.dot(W, numpy.dot(Einv, inner_product(AW, x)))
# --------------------------------------------------------------------------
# cost: (nW^2)*IP
E = inner_product(W, AW)
Einv = numpy.linalg.inv(E)
# cost: nW*IP + (2/3)*nW^3
EWb = numpy.dot(Einv, inner_product(W, b))
# Define projection operator.
N = len(b)
if x0 is None:
x0 = numpy.zeros((N,1))
dtype = upcast(W.dtype, AW.dtype, b.dtype, x0.dtype)
P = LinearOperator( [N,N], Pfun, matmat=Pfun,
dtype=dtype)
# Get updated x0.
# cost: nW*AXPY + cost(Pfun)
x0new = P*x0 + numpy.dot(W, EWb)
return P, x0new
def _mul_sparse_matrix(self, other):
"""
Do the sparse matrix mult returning fast_csr_matrix only
when other is also fast_csr_matrix.
"""
M, _ = self.shape
_, N = other.shape
major_axis = self._swap((M, N))[0]
if isinstance(other, fast_csr_matrix):
A = zcsr_mult(self, other, sorted=1)
return A
other = csr_matrix(other) # convert to this format
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices),
maxval=M * N)
# scipy 1.5 renamed the older csr_matmat_pass1 to the much more
# descriptive csr_matmat_maxnnz, but also changed the call and logic
# structure of constructing the indices.
try:
fn = getattr(_sparsetools, self.format + '_matmat_maxnnz')
nnz = fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype))
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices),
maxval=nnz)
indptr = np.empty(major_axis + 1, dtype=idx_dtype)
except AttributeError:
indptr = np.empty(major_axis + 1, dtype=idx_dtype)
fn = getattr(_sparsetools, self.format + '_matmat_pass1')
fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype), indptr)
nnz = indptr[-1]
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices),
maxval=nnz)
indices = np.empty(nnz, dtype=idx_dtype)
data = np.empty(nnz, dtype=upcast(self.dtype, other.dtype))
try:
fn = getattr(_sparsetools, self.format + '_matmat')
except AttributeError:
fn = getattr(_sparsetools, self.format + '_matmat_pass2')
fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype), self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype), other.data, indptr,
indices, data)
A = csr_matrix((data, indices, indptr), shape=(M, N))
return A
def diagonal(self, k=0):
rows, cols = self.shape
if k <= -rows or k >= cols:
return np.empty(0, dtype=self.data.dtype)
fn = getattr(_sparsetools, self.format + "_diagonal")
y = np.empty(min(rows + min(k, 0), cols - max(k, 0)),
dtype=upcast(self.dtype))
fn(k, self.shape[0], self.shape[1], self.indptr, self.indices,
self.data, y)
return y
def tocsc(self, copy=False):
idx_dtype = get_index_dtype((self.indptr, self.indices),
maxval=max(self.nnz, self.shape[0]))
indptr = np.empty(self.shape[1] + 1, dtype=idx_dtype)
indices = np.empty(self.nnz, dtype=idx_dtype)
data = np.empty(self.nnz, dtype=upcast(self.dtype))
csr_tocsc(self.shape[0], self.shape[1], self.indptr.astype(idx_dtype),
self.indices.astype(idx_dtype), self.data, indptr, indices,
data)
from scipy.sparse.csc import csc_matrix
A = csc_matrix((data, indices, indptr), shape=self.shape)
A.has_sorted_indices = True
return A
def tocsr(self, copy=False):
M, N = self.shape
idx_dtype = get_index_dtype((self.indptr, self.indices),
maxval=max(self.nnz, N))
indptr = np.empty(M + 1, dtype=idx_dtype)
indices = np.empty(self.nnz, dtype=idx_dtype)
data = np.empty(self.nnz, dtype=upcast(self.dtype))
csc_tocsr(M, N, self.indptr.astype(idx_dtype),
self.indices.astype(idx_dtype), self.data, indptr, indices,
data)
from pyomo.contrib.pynumero.sparse.csr import CSRMatrix
A = CSRMatrix((data, indices, indptr), shape=self.shape, copy=False)
A.has_sorted_indices = True
return A
def _binopt(self, other, op):
"""
Do the binary operation fn to two sparse matrices using
fast_csr_matrix only when other is also a fast_csr_matrix.
"""
# e.g. csr_plus_csr, csr_minus_csr, etc.
if not isinstance(other, fast_csr_matrix):
other = csr_matrix(other)
# e.g. csr_plus_csr, csr_minus_csr, etc.
fn = getattr(_sparsetools, self.format + op + self.format)
maxnnz = self.nnz + other.nnz
idx_dtype = get_index_dtype(
(self.indptr, self.indices, other.indptr, other.indices),
maxval=maxnnz)
indptr = np.empty(self.indptr.shape, dtype=idx_dtype)
indices = np.empty(maxnnz, dtype=idx_dtype)
bool_ops = ['_ne_', '_lt_', '_gt_', '_le_', '_ge_']
if op in bool_ops:
data = np.empty(maxnnz, dtype=np.bool_)
else:
data = np.empty(maxnnz, dtype=upcast(self.dtype, other.dtype))
fn(self.shape[0], self.shape[1],
np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype), self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype), other.data, indptr,
indices, data)
actual_nnz = indptr[-1]
indices = indices[:actual_nnz]
data = data[:actual_nnz]
if actual_nnz < maxnnz // 2:
# too much waste, trim arrays
indices = indices.copy()
data = data.copy()
if isinstance(other, fast_csr_matrix) and (not op in bool_ops):
A = fast_csr_matrix((data, indices, indptr),
dtype=data.dtype,
shape=self.shape)
else:
A = csr_matrix((data, indices, indptr),
dtype=data.dtype,
shape=self.shape)
return A
def _mul_sparse_matrix(self, other):
"""
Do the sparse matrix mult returning fast_csr_matrix only
when other is also fast_csr_matrix.
"""
M, K1 = self.shape
K2, N = other.shape
major_axis = self._swap((M,N))[0]
if isinstance(other, fast_csr_matrix):
A = zcsr_mult(self, other)
A.sort_indices()
return A
other = csr_matrix(other) # convert to this format
idx_dtype = get_index_dtype((self.indptr, self.indices,
other.indptr, other.indices),
maxval=M*N)
indptr = np.empty(major_axis + 1, dtype=idx_dtype)
fn = getattr(_sparsetools, self.format + '_matmat_pass1')
fn(M, N,
np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype),
indptr)
nnz = indptr[-1]
idx_dtype = get_index_dtype((self.indptr, self.indices,
other.indptr, other.indices),
maxval=nnz)
indptr = np.asarray(indptr, dtype=idx_dtype)
indices = np.empty(nnz, dtype=idx_dtype)
data = np.empty(nnz, dtype=upcast(self.dtype, other.dtype))
fn = getattr(_sparsetools, self.format + '_matmat_pass2')
fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype),
other.data,
indptr, indices, data)
A = csr_matrix((data,indices,indptr),shape=(M,N))
return A
def coo_tocsr(coo_mat):
M, N = coo_mat.shape
idx_dtype = get_index_dtype((coo_mat.row, coo_mat.col),
maxval=max(coo_mat.nnz, N))
indptr = np.empty(M + 1, dtype=idx_dtype)
indices = np.empty(coo_mat.nnz, dtype=idx_dtype)
data = np.empty(coo_mat.nnz, dtype=upcast(coo_mat.dtype))
scipy_coo_tocsr(M, N, coo_mat.nnz, coo_mat.row.astype(idx_dtype),
coo_mat.col.astype(idx_dtype), coo_mat.data, indptr,
indices, data)
A = scipy.sparse.csr_matrix((data, indices, indptr), shape=coo_mat.shape)
A.sort_indices()
csr_max_duplicates(M, N, A.indptr, A.indices, A.data)
A.prune()
A.has_canonical_format = True
return A
def _binopt(self, other, op):
"""
Do the binary operation fn to two sparse matrices using
fast_csr_matrix only when other is also a fast_csr_matrix.
"""
# e.g. csr_plus_csr, csr_minus_csr, etc.
if not isinstance(other, fast_csr_matrix):
other = csr_matrix(other)
# e.g. csr_plus_csr, csr_minus_csr, etc.
fn = getattr(_sparsetools, self.format + op + self.format)
maxnnz = self.nnz + other.nnz
idx_dtype = get_index_dtype((self.indptr, self.indices,
other.indptr, other.indices),
maxval=maxnnz)
indptr = np.empty(self.indptr.shape, dtype=idx_dtype)
indices = np.empty(maxnnz, dtype=idx_dtype)
bool_ops = ['_ne_', '_lt_', '_gt_', '_le_', '_ge_']
if op in bool_ops:
data = np.empty(maxnnz, dtype=np.bool_)
else:
data = np.empty(maxnnz, dtype=upcast(self.dtype, other.dtype))
fn(self.shape[0], self.shape[1],
np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype),
other.data,
indptr, indices, data)
actual_nnz = indptr[-1]
indices = indices[:actual_nnz]
data = data[:actual_nnz]
if actual_nnz < maxnnz // 2:
# too much waste, trim arrays
indices = indices.copy()
data = data.copy()
if isinstance(other, fast_csr_matrix) and (not op in bool_ops):
A = fast_csr_matrix((data, indices, indptr), dtype=data.dtype, shape=self.shape)
else:
A = csr_matrix((data, indices, indptr), dtype=data.dtype, shape=self.shape)
return A
def _mul_sparse_matrix(self, other):
"""
Do the sparse matrix mult returning fast_csr_matrix only
when other is also fast_csr_matrix.
"""
M, _ = self.shape
_, N = other.shape
major_axis = self._swap((M, N))[0]
if isinstance(other, fast_csr_matrix):
A = zcsr_mult(self, other, sorted=1)
return A
other = csr_matrix(other) # convert to this format
idx_dtype = get_index_dtype((self.indptr, self.indices,
other.indptr, other.indices),
maxval=M * N)
indptr = np.empty(major_axis + 1, dtype=idx_dtype)
fn = getattr(_sparsetools, self.format + '_matmat_pass1')
fn(M, N,
np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype),
indptr)
nnz = indptr[-1]
idx_dtype = get_index_dtype((self.indptr, self.indices,
other.indptr, other.indices),
maxval=nnz)
indptr = np.asarray(indptr, dtype=idx_dtype)
indices = np.empty(nnz, dtype=idx_dtype)
data = np.empty(nnz, dtype=upcast(self.dtype, other.dtype))
fn = getattr(_sparsetools, self.format + '_matmat_pass2')
fn(M, N, np.asarray(self.indptr, dtype=idx_dtype),
np.asarray(self.indices, dtype=idx_dtype),
self.data,
np.asarray(other.indptr, dtype=idx_dtype),
np.asarray(other.indices, dtype=idx_dtype),
other.data,
indptr, indices, data)
A = csr_matrix((data, indices, indptr), shape=(M, N))
return A
def coo_tocsr(coo_mat):
M, N = coo_mat.shape
idx_dtype = get_index_dtype((coo_mat.row, coo_mat.col),
maxval=max(coo_mat.nnz, N))
indptr = np.empty(M + 1, dtype=idx_dtype)
indices = np.empty(coo_mat.nnz, dtype=idx_dtype)
data = np.empty(coo_mat.nnz, dtype=upcast(coo_mat.dtype))
scipy_coo_tocsr(M, N, coo_mat.nnz,
coo_mat.row.astype(idx_dtype),
coo_mat.col.astype(idx_dtype),
coo_mat.data,
indptr, indices, data)
A = scipy.sparse.csr_matrix((data, indices, indptr), shape=coo_mat.shape)
A.sort_indices()
csr_max_duplicates(M, N, A.indptr, A.indices, A.data)
A.prune()
A.has_canonical_format = True
return A
def tocsr(self):
"""Return a copy of this matrix in Compressed Sparse Row format
Duplicate entries will be summed together.
Examples
--------
>>> from numpy import array
>>> from scipy.sparse import coo_matrix
>>> row = array([0, 0, 1, 3, 1, 0, 0])
>>> col = array([0, 2, 1, 3, 1, 0, 0])
>>> data = array([1, 1, 1, 1, 1, 1, 1])
>>> A = coo_matrix((data, (row, col)), shape=(4, 4)).tocsr()
>>> A.toarray()
array([[3, 0, 1, 0],
[0, 2, 0, 0],
[0, 0, 0, 0],
[0, 0, 0, 1]])
"""
from .csr import csr_matrix
if self.nnz == 0:
return csr_matrix(self.shape, dtype=self.dtype)
else:
M, N = self.shape
idx_dtype = get_index_dtype((self.row, self.col),
maxval=max(self.nnz, N))
indptr = np.empty(M + 1, dtype=idx_dtype)
indices = np.empty(self.nnz, dtype=idx_dtype)
data = np.empty(self.nnz, dtype=upcast(self.dtype))
coo_tocsr(M, N, self.nnz, self.row.astype(idx_dtype),
self.col.astype(idx_dtype), self.data, indptr, indices,
data)
A = csr_matrix((data, indices, indptr), shape=self.shape)
A.sum_duplicates()
return A
def test_upcast(self):
assert_equal(sputils.upcast('intc'),np.intc)
assert_equal(sputils.upcast('int32','float32'),np.float64)
assert_equal(sputils.upcast('bool',complex,float),np.complex128)
assert_equal(sputils.upcast('i','d'),np.float64)
def cgne(A,
b,
x0=None,
tol=1e-5,
maxiter=None,
xtype=None,
M=None,
callback=None,
residuals=None):
'''Conjugate Gradient, Normal Error algorithm
Applies CG to the normal equations, A.H A x = b. Left preconditioning
is supported. Note that unless A is well-conditioned, the use of
CGNE is inadvisable
Parameters
----------
A : {array, matrix, sparse matrix, LinearOperator}
n x n, linear system to solve
b : {array, matrix}
right hand side, shape is (n,) or (n,1)
x0 : {array, matrix}
initial guess, default is a vector of zeros
tol : float
relative convergence tolerance, i.e. tol is scaled by ||r_0||_2
maxiter : int
maximum number of allowed iterations
xtype : type
dtype for the solution, default is automatic type detection
M : {array, matrix, sparse matrix, LinearOperator}
n x n, inverted preconditioner, i.e. solve M A A.H x = M b.
callback : function
User-supplied function is called after each iteration as
callback(xk), where xk is the current solution vector
residuals : list
residuals has the residual norm history,
including the initial residual, appended to it
Returns
-------
(xNew, info)
xNew : an updated guess to the solution of Ax = b
info : halting status of cgne
== =======================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead.
<0 numerical breakdown, or illegal input
== =======================================
Notes
-----
- The LinearOperator class is in scipy.sparse.linalg.interface.
Use this class if you prefer to define A or M as a mat-vec routine
as opposed to explicitly constructing the matrix. A.psolve(..) is
still supported as a legacy.
Examples
--------
>>> from pyamg.krylov.cgne import cgne
>>> from pyamg.util.linalg import norm
>>> import numpy as np
>>> from pyamg.gallery import poisson
>>> A = poisson((10,10))
>>> b = np.ones((A.shape[0],))
>>> (x,flag) = cgne(A,b, maxiter=2, tol=1e-8)
>>> print norm(b - A*x)
46.1547104367
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 276-7, 2003
http://www-users.cs.umn.edu/~saad/books.html
'''
# Store the conjugate transpose explicitly as it will be used much later on
if isspmatrix(A):
AH = A.H
else:
# TODO avoid doing this since A may be a different sparse type
AH = aslinearoperator(np.asmatrix(A).H)
# Convert inputs to linear system, with error checking
A, M, x, b, postprocess = make_system(A, M, x0, b, xtype)
dimen = A.shape[0]
# Ensure that warnings are always reissued from this function
import warnings
warnings.filterwarnings('always', module='pyamg\.krylov\._cgne')
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
if not hasattr(M, 'dtype'):
Mtype = upcast(x.dtype, b.dtype)
else:
Mtype = M.dtype
xtype = upcast(Atype, x.dtype, b.dtype, Mtype)
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# How often should r be recomputed
recompute_r = 8
# Check iteration numbers. CGNE suffers from loss of orthogonality quite
# easily, so we arbitrarily let the method go up to 130% over the
# theoretically necessary limit of maxiter=dimen
if maxiter is None:
maxiter = int(np.ceil(1.3 * dimen)) + 2
elif maxiter < 1:
raise ValueError('Number of iterations must be positive')
elif maxiter > (1.3 * dimen):
warn('maximum allowed inner iterations (maxiter) are the 130% times \
the number of dofs')
maxiter = int(np.ceil(1.3 * dimen)) + 2
# Prep for method
r = b - A * x
normr = norm(r)
if keep_r:
residuals.append(normr)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol * normb:
if callback is not None:
callback(x)
return (postprocess(x), 0)
# Scale tol by ||r_0||_2
if normr != 0.0:
tol = tol * normr
# Begin CGNE
# Apply preconditioner and calculate initial search direction
z = M * r
p = AH * z
old_zr = np.inner(z.conjugate(), r)
for iter in range(maxiter):
# alpha = (z_j, r_j) / (p_j, p_j)
alpha = old_zr / np.inner(p.conjugate(), p)
# x_{j+1} = x_j + alpha*p_j
x += alpha * p
# r_{j+1} = r_j - alpha*w_j, where w_j = A*p_j
if np.mod(iter, recompute_r) and iter > 0:
r -= alpha * (A * p)
else:
r = b - A * x
# z_{j+1} = M*r_{j+1}
z = M * r
# beta = (z_{j+1}, r_{j+1}) / (z_j, r_j)
new_zr = np.inner(z.conjugate(), r)
beta = new_zr / old_zr
old_zr = new_zr
# p_{j+1} = A.H*z_{j+1} + beta*p_j
p *= beta
p += AH * z
# Allow user access to residual
if callback is not None:
callback(x)
# test for convergence
normr = norm(r)
if keep_r:
residuals.append(normr)
if normr < tol:
return (postprocess(x), 0)
# end loop
return (postprocess(x), iter + 1)
def fgmres(A, b, x0=None, tol=1e-5, restrt=None, maxiter=None, xtype=None,
M=None, callback=None, residuals=None):
'''Flexible Generalized Minimum Residual Method (fGMRES)
fGMRES iteratively refines the initial solution guess to the
system Ax = b. fGMRES is flexible in the sense that the right
preconditioner (M) can vary from iteration to iteration.
Parameters
----------
A : {array, matrix, sparse matrix, LinearOperator}
n x n, linear system to solve
b : {array, matrix}
right hand side, shape is (n,) or (n,1)
x0 : {array, matrix}
initial guess, default is a vector of zeros
tol : float
relative convergence tolerance, i.e. tol is scaled by ||r_0||_2
restrt : {None, int}
- if int, restrt is max number of inner iterations
and maxiter is the max number of outer iterations
- if None, do not restart GMRES, and max number of inner iterations is
maxiter
maxiter : {None, int}
- if restrt is None, maxiter is the max number of inner iterations
and GMRES does not restart
- if restrt is int, maxiter is the max number of outer iterations,
and restrt is the max number of inner iterations
xtype : type
dtype for the solution, default is automatic type detection
M : {array, matrix, sparse matrix, LinearOperator}
n x n, inverted preconditioner, i.e. solve A M x = M b.
M need not be stationary for fgmres
callback : function
User-supplied function is called after each iteration as
callback( ||rk||_2 ), where rk is the current residual vector
residuals : list
residuals has the residual norm history,
including the initial residual, appended to it
Returns
-------
(xNew, info)
xNew : an updated guess to the solution of Ax = b
info : halting status of gmres
== =============================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead. This value
is precisely the order of the Krylov space.
<0 numerical breakdown, or illegal input
== =============================================
Notes
-----
- The LinearOperator class is in scipy.sparse.linalg.interface.
Use this class if you prefer to define A or M as a mat-vec routine
as opposed to explicitly constructing the matrix. A.psolve(..) is
still supported as a legacy.
- fGMRES allows for non-stationary preconditioners, as opposed to GMRES
- For robustness, Householder reflections are used to orthonormalize
the Krylov Space
Givens Rotations are used to provide the residual norm each iteration
Flexibility implies that the right preconditioner, M or A.psolve, can
vary from iteration to iteration
Examples
--------
>>> from pyamg.krylov.fgmres import fgmres
>>> from pyamg.util.linalg import norm
>>> import numpy as np
>>> from pyamg.gallery import poisson
>>> A = poisson((10,10))
>>> b = np.ones((A.shape[0],))
>>> (x,flag) = fgmres(A,b, maxiter=2, tol=1e-8)
>>> print norm(b - A*x)
6.5428213057
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
http://www-users.cs.umn.edu/~saad/books.html
'''
# Convert inputs to linear system, with error checking
A, M, x, b, postprocess = make_system(A, M, x0, b, xtype)
dimen = A.shape[0]
# Ensure that warnings are always reissued from this function
import warnings
warnings.filterwarnings('always', module='pyamg\.krylov\._fgmres')
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
if not hasattr(M, 'dtype'):
Mtype = upcast(x.dtype, b.dtype)
else:
Mtype = M.dtype
xtype = upcast(Atype, x.dtype, b.dtype, Mtype)
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# Set number of outer and inner iterations
if restrt:
if maxiter:
max_outer = maxiter
else:
max_outer = 1
if restrt > dimen:
warn('Setting number of inner iterations (restrt) to maximum \
allowed, which is A.shape[0] ')
restrt = dimen
max_inner = restrt
else:
max_outer = 1
if maxiter > dimen:
warn('Setting number of inner iterations (maxiter) to maximum \
allowed, which is A.shape[0] ')
maxiter = dimen
elif maxiter is None:
maxiter = min(dimen, 40)
max_inner = maxiter
# Get fast access to underlying BLAS routines
[rotg] = get_blas_funcs(['rotg'], [x])
# Is this a one dimensional matrix?
if dimen == 1:
entry = ravel(A*array([1.0], dtype=xtype))
return (postprocess(b/entry), 0)
# Prep for method
r = b - ravel(A*x)
normr = norm(r)
if keep_r:
residuals.append(normr)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol*normb:
if callback is not None:
callback(norm(r))
return (postprocess(x), 0)
# Scale tol by ||r_0||_2, we don't use the preconditioned
# residual because this is right preconditioned GMRES.
if normr != 0.0:
tol = tol*normr
# Use separate variable to track iterations. If convergence fails,
# we cannot simply report niter = (outer-1)*max_outer + inner. Numerical
# error could cause the inner loop to halt while the actual ||r|| > tol.
niter = 0
# Begin fGMRES
for outer in range(max_outer):
# Calculate vector w, which defines the Householder reflector
# Take shortcut in calculating,
# w = r + sign(r[1])*||r||_2*e_1
w = r
beta = mysign(w[0])*normr
w[0] += beta
w /= norm(w)
# Preallocate for Krylov vectors, Householder reflectors and Hessenberg
# matrix
# Space required is O(dimen*max_inner)
# Givens Rotations
Q = zeros((4*max_inner,), dtype=xtype)
# upper Hessenberg matrix (made upper tri with Givens Rotations)
H = zeros((max_inner, max_inner), dtype=xtype)
W = zeros((max_inner, dimen), dtype=xtype) # Householder reflectors
# For fGMRES, preconditioned vectors must be stored
# No Horner-like scheme exists that allow us to avoid this
Z = zeros((dimen, max_inner), dtype=xtype)
W[0, :] = w
# Multiply r with (I - 2*w*w.T), i.e. apply the Householder reflector
# This is the RHS vector for the problem in the Krylov Space
g = zeros((dimen,), dtype=xtype)
g[0] = -beta
for inner in range(max_inner):
# Calculate Krylov vector in two steps
# (1) Calculate v = P_j = (I - 2*w*w.T)v, where k = inner
v = -2.0*conjugate(w[inner])*w
v[inner] += 1.0
# (2) Calculate the rest, v = P_1*P_2*P_3...P_{j-1}*ej.
# for j in range(inner-1,-1,-1):
# v = v - 2.0*dot(conjugate(W[j,:]), v)*W[j,:]
amg_core.apply_householders(v, ravel(W), dimen, inner-1, -1, -1)
# Apply preconditioner
v = ravel(M*v)
# Check for nan, inf
# if isnan(v).any() or isinf(v).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
Z[:, inner] = v
# Calculate new search direction
v = ravel(A*v)
# Factor in all Householder orthogonal reflections on new search
# direction
# for j in range(inner+1):
# v = v - 2.0*dot(conjugate(W[j,:]), v)*W[j,:]
amg_core.apply_householders(v, ravel(W), dimen, 0, inner+1, 1)
# Calculate next Householder reflector, w
# w = v[inner+1:] + sign(v[inner+1])*||v[inner+1:]||_2*e_{inner+1)
# Note that if max_inner = dimen, then this is unnecessary for
# the last inner iteration, when inner = dimen-1. Here we do
# not need to calculate a Householder reflector or Givens
# rotation because nnz(v) is already the desired length,
# i.e. we do not need to zero anything out.
if inner != dimen-1:
if inner < (max_inner-1):
w = W[inner+1, :]
vslice = v[inner+1:]
alpha = norm(vslice)
if alpha != 0:
alpha = mysign(vslice[0])*alpha
# do not need the final reflector for future calculations
if inner < (max_inner-1):
w[inner+1:] = vslice
w[inner+1] += alpha
w /= norm(w)
# Apply new reflector to v
# v = v - 2.0*w*(w.T*v)
v[inner+1] = -alpha
v[inner+2:] = 0.0
if inner > 0:
# Apply all previous Givens Rotations to v
amg_core.apply_givens(Q, v, dimen, inner)
# Calculate the next Givens rotation, where j = inner Note that if
# max_inner = dimen, then this is unnecessary for the last inner
# iteration, when inner = dimen-1. Here we do not need to
# calculate a Householder reflector or Givens rotation because
# nnz(v) is already the desired length, i.e. we do not need to zero
# anything out.
if inner != dimen-1:
if v[inner+1] != 0:
[c, s] = rotg(v[inner], v[inner+1])
Qblock = array([[c, s], [-conjugate(s), c]], dtype=xtype)
Q[(inner*4): ((inner+1)*4)] = ravel(Qblock).copy()
# Apply Givens Rotation to g, the RHS for the linear system
# in the Krylov Subspace. Note that this dot does a matrix
# multiply, not an actual dot product where a conjugate
# transpose is taken
g[inner:inner+2] = dot(Qblock, g[inner:inner+2])
# Apply effect of Givens Rotation to v
v[inner] = dot(Qblock[0, :], v[inner:inner+2])
v[inner+1] = 0.0
# Write to upper Hessenberg Matrix,
# the LHS for the linear system in the Krylov Subspace
H[:, inner] = v[0:max_inner]
# Don't update normr if last inner iteration, because
# normr is calculated directly after this loop ends.
if inner < max_inner-1:
normr = abs(g[inner+1])
if normr < tol:
break
# Allow user access to residual
if callback is not None:
callback(normr)
if keep_r:
residuals.append(normr)
niter += 1
# end inner loop, back to outer loop
# Find best update to x in Krylov Space, V. Solve inner+1 x inner+1
# system. Apparently this is the best way to solve a triangular system
# in the magical world of scipy
# piv = arange(inner+1)
# y = lu_solve((H[0:(inner+1),0:(inner+1)], piv),
# g[0:(inner+1)], trans=0)
y = sp.linalg.solve(H[0:(inner+1), 0:(inner+1)], g[0:(inner+1)])
# No Horner like scheme exists because the preconditioner can change
# each iteration # Hence, we must store each preconditioned vector
update = dot(Z[:, 0:inner+1], y)
x = x + update
r = b - ravel(A*x)
normr = norm(r)
# Allow user access to residual
if callback is not None:
callback(normr)
if keep_r:
residuals.append(normr)
# Has fGMRES stagnated?
indices = (x != 0)
if indices.any():
change = max(abs(update[indices] / x[indices]))
if change < 1e-12:
# No change, halt
return (postprocess(x), -1)
# test for convergence
if normr < tol:
return (postprocess(x), 0)
# end outer loop
return (postprocess(x), niter)
m2 = np.random.randint(0, 100, (m, n))
m2[m2 > 50] = 0
m1x = sparse.csr_matrix(m1)
m2x = sparse.csr_matrix(m2)
maxnnz = m1x.nnz + m2x.nnz
idx_dtype = get_index_dtype((m1x.indptr, m1x.indices, m2x.indptr, m2x.indices),
maxval=maxnnz)
indptr = np.empty(m1x.indptr.shape, dtype=idx_dtype)
indices = np.empty(maxnnz, dtype=idx_dtype)
bool_ops = ['_ne_', '_lt_', '_gt_', '_le_', '_ge_']
if 'enul' in bool_ops:
data = np.empty(maxnnz, dtype=np.bool_)
else:
data = np.empty(maxnnz, dtype=upcast(m1x.dtype, m2x.dtype))
n_row, n_col = m1.shape
Ap = m1x.indptr
Aj = m1x.indices
Ax = m1x.data
Bp = m2x.indptr
Bj = m2x.indices
Bx = m2x.data
Cp = indptr
Cj = indices
Cx = data
loops = [100, 500, 1000]
tb = PrettyTable()
tb.field_names = [""] + ["{} loops".format(loop) for loop in loops]
def gmres_mgs(A, x, b, R, tol, max_iter):
"""
Generalized Minimum Residual Method (GMRES)
GMRES iteratively refines the initial solution guess to the system
Ax = b
Modified Gram-Schmidt version
Parameter
---------
A : matrix, n x n, matrix from the linear system to solve.
x : array, initial guess.
b : array, right hand side.
R : int, number of iterations for GMRES to do restart.
tol : float, convergence tolerance.
max_iter: int, maximum number of GMRES iterations.
Returns
-------
x : array, an updated guess to the solution of Ax = b.
"""
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
xtype = upcast(Atype, x.dtype, b.dtype)
# Get fast access to underlying BLAS routines
# dotc is the conjugate dot, dotu does no conjugation
if numpy.iscomplexobj(numpy.zeros((1, ), dtype=xtype)):
[axpy, dotu, dotc, scal, rotg] =\
get_blas_funcs(['axpy', 'dotu', 'dotc', 'scal', 'rotg'], [x])
else:
# real type
[axpy, dotu, dotc, scal, rotg] =\
get_blas_funcs(['axpy', 'dot', 'dot', 'scal', 'rotg'], [x])
# Make full use of direct access to BLAS by defining own norm
def norm(z):
return numpy.sqrt(numpy.real(dotc(z, z)))
#Defining dimension
dimen = A.shape[0]
# Set number of outer and inner iterations
max_outer = max_iter
if R > dimen:
warn('Setting number of inner iterations (restrt) to maximum\
allowed, which is A.shape[0] ')
R = dimen
max_inner = R
# Prep for method
r = b - scipy.dot(A, x)
normr = norm(r)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol * normb:
return x
iteration = 0
#Here start the GMRES
for outer in range(max_outer):
# Preallocate for Givens Rotations, Hessenberg matrix and Krylov Space
# Space required is O(dimen*max_inner).
# NOTE: We are dealing with row-major matrices, so we traverse in a
# row-major fashion,
# i.e., H and V's transpose is what we store.
Q = [] # Initialzing Givens Rotations
# Upper Hessenberg matrix, which is then
# converted to upper triagonal with Givens Rotations
H = numpy.zeros((max_inner + 1, max_inner + 1), dtype=xtype)
V = numpy.zeros((max_inner + 1, dimen), dtype=xtype) #Krylov space
# vs store the pointers to each column of V.
# This saves a considerable amount of time.
vs = []
# v = r/normr
V[0, :] = scal(1.0 / normr, r) # scal wrapper of dscal --> x = a*x
vs.append(V[0, :])
#Saving initial residual to be used to calculate the rel_resid
if iteration == 0:
res_0 = normb
#RHS vector in the Krylov space
g = numpy.zeros((dimen, ), dtype=xtype)
g[0] = normr
for inner in range(max_inner):
#New search direction
v = V[inner + 1, :]
v[:] = scipy.dot(A, vs[-1])
vs.append(v)
normv_old = norm(v)
#Modified Gram Schmidt
for k in range(inner + 1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = alpha
v[:] = axpy(vk, v, dimen, -alpha) # y := a*x + y
#axpy is a wrapper for daxpy (blas function)
normv = norm(v)
H[inner, inner + 1] = normv
#Check for breakdown
if H[inner, inner + 1] != 0.0:
v[:] = scal(1.0 / H[inner, inner + 1], v)
#Apply for Givens rotations to H
if inner > 0:
apply_givens(Q, H[inner, :], inner)
#Calculate and apply next complex-valued Givens rotations
#If max_inner = dimen, we don't need to calculate, this
#is unnecessary for the last inner iteration when inner = dimen -1
if inner != dimen - 1:
if H[inner, inner + 1] != 0:
#rotg is a blas function that computes the parameters
#for a Givens rotation
[c, s] = rotg(H[inner, inner], H[inner, inner + 1])
Qblock = numpy.array([[c, s], [-numpy.conjugate(s), c]],
dtype=xtype)
Q.append(Qblock)
#Apply Givens Rotations to RHS for the linear system in
# the krylov space.
g[inner:inner + 2] = scipy.dot(Qblock, g[inner:inner + 2])
#Apply Givens rotations to H
H[inner, inner] = dotu(Qblock[0, :], H[inner,
inner:inner + 2])
H[inner, inner + 1] = 0.0
iteration += 1
if inner < max_inner - 1:
normr = abs(g[inner + 1])
rel_resid = normr / res_0
if rel_resid < tol:
break
if iteration % 1 == 0:
print('Iteration: %i, relative residual: %s' %
(iteration, rel_resid))
if (inner + 1 == R):
print('Residual: %f. Restart...' % rel_resid)
# end inner loop, back to outer loop
# Find best update to x in Krylov Space V. Solve inner x inner system.
y = scipy.linalg.solve(H[0:inner + 1, 0:inner + 1].T, g[0:inner + 1])
update = numpy.ravel(scipy.mat(V[:inner + 1, :]).T * y.reshape(-1, 1))
x = x + update
r = b - scipy.dot(A, x)
normr = norm(r)
rel_resid = normr / res_0
# test for convergence
if rel_resid < tol:
print('Converged after %i iterations to a residual of %s' %
(iteration, rel_resid))
return x
#end outer loop
return x
def gmres(A, b, x0=None, tol=1e-5, restrt=None, maxiter=None, xtype=None, M=None, callback=None, residuals=None):
'''
Generalized Minimum Residual Method (GMRES)
GMRES iteratively refines the initial solution guess to the system Ax = b
For robustness, Householder reflections are used to orthonormalize the Krylov Space
Givens Rotations are used to provide the residual norm each iteration
Parameters
----------
A : array, matrix or sparse matrix
n x n, linear system to solve
b : array
n x 1, right hand side
x0 : array
n x 1, initial guess
default is a vector of zeros
tol : float
convergence tolerance
restrt : int
number of restarts
total iterations = restrt*maxiter
maxiter : int
maximum number of allowed inner iterations
xtype : type
dtype for the solution
M : matrix-like
n x n, inverted preconditioner, i.e. solve M A x = b.
For preconditioning with a mat-vec routine, set
A.psolve = func, where func := M y
callback : function
callback( ||resid||_2 ) is called each iteration,
residuals : {None, empty-list}
If empty-list, residuals holds the residual norm history,
including the initial residual, upon completion
Returns
-------
(xNew, info)
xNew -- an updated guess to the solution of Ax = b
info -- halting status of gmres
0 : successful exit
>0 : convergence to tolerance not achieved,
return iteration count instead. This value
is precisely the order of the Krylov space.
<0 : numerical breakdown, or illegal input
Notes
-----
Examples
--------
>>>from pyamg.krylov import *
>>>from scipy import rand
>>>import pyamg
>>>A = pyamg.poisson((50,50))
>>>b = rand(A.shape[0],)
>>>(x,flag) = gmres(A,b)
>>>print pyamg.util.linalg.norm(b - A*x)
References
----------
Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
'''
# Convert inputs to linear system, with error checking
A,M,x,b,postprocess = make_system(A,M,x0,b,xtype)
dimen = A.shape[0]
# Choose type
xtype = upcast(A.dtype, x.dtype, b.dtype, M.dtype)
# We assume henceforth that shape=(n,) for all arrays
b = ravel(array(b,xtype))
x = ravel(array(x,xtype))
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# check number of iterations
if restrt == None:
restrt = 1
elif restrt < 1:
raise ValueError('Number of restarts must be positive')
if maxiter == None:
maxiter = int(max(ceil(dimen/restrt)))
elif maxiter < 1:
raise ValueError('Number of iterations must be positive')
elif maxiter > dimen:
warn('maximimum allowed inner iterations (maxiter) are the number of degress of freedom')
maxiter = dimen
# Scale tol by normb
normb = linalg.norm(b)
if normb == 0:
pass
# if callback != None:
# callback(0.0)
#
# return (postprocess(zeros((dimen,)), dtype=xtype),0)
else:
tol = tol*normb
# Is this a one dimensional matrix?
if dimen == 1:
entry = ravel(A*array([1.0], dtype=xtype))
return (postprocess(b/entry), 0)
# Prep for method
r = b - ravel(A*x)
normr = linalg.norm(r)
if keep_r:
residuals.append(normr)
# Is initial guess sufficient?
if normr <= tol:
if callback != None:
callback(norm(r))
return (postprocess(x), 0)
#Apply preconditioner
r = ravel(M*r)
normr = linalg.norm(r)
# Check for nan, inf
if any(isnan(r)) or any(isinf(r)):
warn('inf or nan after application of preconditioner')
return(postprocess(x), -1)
# Use separate variable to track iterations. If convergence fails, we cannot
# simply report niter = (outer-1)*maxiter + inner. Numerical error could cause
# the inner loop to halt before reaching maxiter while the actual ||r|| > tol.
niter = 0
# Begin GMRES
for outer in range(restrt):
# Calculate vector w, which defines the Householder reflector
# Take shortcut in calculating,
# w = r + sign(r[1])*||r||_2*e_1
w = r
beta = mysign(w[0])*normr
w[0] += beta
w = w / linalg.norm(w)
# Preallocate for Krylov vectors, Householder reflectors and Hessenberg matrix
# Space required is O(dimen*maxiter)
H = zeros( (maxiter, maxiter), dtype=xtype) # upper Hessenberg matrix (actually made upper tri with Given's Rotations)
W = zeros( (dimen, maxiter), dtype=xtype) # Householder reflectors
W[:,0] = w
# Multiply r with (I - 2*w*w.T), i.e. apply the Householder reflector
# This is the RHS vector for the problem in the Krylov Space
g = zeros((dimen,), dtype=xtype)
g[0] = -beta
for inner in range(maxiter):
# Calcute Krylov vector in two steps
# (1) Calculate v = P_j = (I - 2*w*w.T)v, where k = inner
v = -2.0*conjugate(w[inner])*w
v[inner] += 1.0
# (2) Calculate the rest, v = P_1*P_2*P_3...P_{j-1}*ej.
for j in range(inner-1,-1,-1):
v = v - 2.0*dot(conjugate(W[:,j]), v)*W[:,j]
# Calculate new search direction
v = ravel(A*v)
#Apply preconditioner
v = ravel(M*v)
# Check for nan, inf
if any(isnan(v)) or any(isinf(v)):
warn('inf or nan after application of preconditioner')
return(postprocess(x), -1)
# Factor in all Householder orthogonal reflections on new search direction
for j in range(inner+1):
v = v - 2.0*dot(conjugate(W[:,j]), v)*W[:,j]
# Calculate next Householder reflector, w
# w = v[inner+1:] + sign(v[inner+1])*||v[inner+1:]||_2*e_{inner+1)
# Note that if maxiter = dimen, then this is unnecessary for the last inner
# iteration, when inner = dimen-1. Here we do not need to calculate a
# Householder reflector or Given's rotation because nnz(v) is already the
# desired length, i.e. we do not need to zero anything out.
if inner != dimen-1:
w = zeros((dimen,), dtype=xtype)
vslice = v[inner+1:]
alpha = linalg.norm(vslice)
if alpha != 0:
alpha = mysign(vslice[0])*alpha
# We do not need the final reflector for future calculations
if inner < (maxiter-1):
w[inner+1:] = vslice
w[inner+1] += alpha
w = w / linalg.norm(w)
W[:,inner+1] = w
# Apply new reflector to v
# v = v - 2.0*w*(w.T*v)
v[inner+1] = -alpha
v[inner+2:] = 0.0
# Apply all previous Given's Rotations to v
if inner == 0:
# Q will store the cumulative effect of all Given's Rotations
Q = scipy.sparse.eye(dimen, dimen, format='csr', dtype=xtype)
# Declare initial Qj, which will be the current Given's Rotation
rowptr = hstack( (array([0, 2, 4],int), arange(5,dimen+3,dtype=int)) )
colindices = hstack( (array([0, 1, 0, 1],int), arange(2, dimen,dtype=int)) )
data = ones((dimen+2,), dtype=xtype)
Qj = csr_matrix( (data, colindices, rowptr), shape=(dimen,dimen), dtype=xtype)
else:
# Could avoid building a global Given's Rotation, by storing
# and applying each 2x2 matrix individually.
# But that would require looping, the bane of wonderful Python
Q = Qj*Q
v = Q*v
# Calculate Qj, the next Given's rotation, where j = inner
# Note that if maxiter = dimen, then this is unnecessary for the last inner
# iteration, when inner = dimen-1. Here we do not need to calculate a
# Householder reflector or Given's rotation because nnz(v) is already the
# desired length, i.e. we do not need to zero anything out.
if inner != dimen-1:
if v[inner+1] != 0:
# Calculate terms for complex 2x2 Given's Rotation
# Note that abs(x) takes the complex modulus
h1 = v[inner]; h2 = v[inner+1];
h1_mag = abs(h1); h2_mag = abs(h2);
if h1_mag < h2_mag:
mu = h1/h2
tau = conjugate(mu)/abs(mu)
else:
mu = h2/h1
tau = mu/abs(mu)
denom = sqrt( h1_mag**2 + h2_mag**2 )
c = h1_mag/denom; s = h2_mag*tau/denom;
Qblock = array([[c, conjugate(s)], [-s, c]], dtype=xtype)
# Modify Qj in csr-format so that it represents the current
# global Given's Rotation equivalent to Qblock
if inner != 0:
Qj.data[inner-1] = 1.0
Qj.indices[inner-1] = inner-1
Qj.indptr[inner-1] = inner-1
Qj.data[inner:inner+4] = ravel(Qblock)
Qj.indices[inner:inner+4] = [inner, inner+1, inner, inner+1]
Qj.indptr[inner:inner+3] = [inner, inner+2, inner+4]
# Apply Given's Rotation to g,
# the RHS for the linear system in the Krylov Subspace.
# Note that this dot does a matrix multiply, not an actual
# dot product where a conjugate transpose is taken
g[inner:inner+2] = dot(Qblock, g[inner:inner+2])
# Apply effect of Given's Rotation to v
v[inner] = dot(Qblock[0,:], v[inner:inner+2])
v[inner+1] = 0.0
# Write to upper Hessenberg Matrix,
# the LHS for the linear system in the Krylov Subspace
H[:,inner] = v[0:maxiter]
# Don't update normr if last inner iteration, because
# normr is calculated directly after this loop ends.
if inner < maxiter-1:
normr = abs(g[inner+1])
if normr < tol:
break
# Allow user access to residual
if callback != None:
callback( normr )
if keep_r:
residuals.append(normr)
niter += 1
# end inner loop, back to outer loop
# Find best update to x in Krylov Space, V. Solve inner+1 x inner+1 system.
# Apparently this is the best way to solve a triangular
# system in the magical world of scipy
piv = arange(inner+1)
y = lu_solve((H[0:(inner+1),0:(inner+1)], piv), g[0:(inner+1)], trans=0)
# Use Horner like Scheme to map solution, y, back to original space.
# Note that we do not use the last reflector.
update = zeros(x.shape, dtype=xtype)
for j in range(inner,-1,-1):
update[j] += y[j]
# Apply j-th reflector, (I - 2.0*w_j*w_j.T)*upadate
update = update - 2.0*dot(conjugate(W[:,j]), update)*W[:,j]
x = x + update
r = b - ravel(A*x)
#Apply preconditioner
r = ravel(M*r)
normr = linalg.norm(r)
# Check for nan, inf
if any(isnan(r)) or any(isinf(r)):
warn('inf or nan after application of preconditioner')
return(postprocess(x), -1)
# Allow user access to residual
if callback != None:
callback( normr )
if keep_r:
residuals.append(normr)
# Has GMRES stagnated?
indices = (x != 0)
if indices.any():
change = max(abs( update[indices] / x[indices] ))
if change < 1e-12:
# No change, halt
return (postprocess(x), -1)
# test for convergence
if normr < tol:
return (postprocess(x),0)
# end outer loop
return (postprocess(x), niter)
def gmres_householder(A,
b,
x0=None,
tol=1e-5,
restrt=None,
maxiter=None,
xtype=None,
M=None,
callback=None,
residuals=None):
'''
Generalized Minimum Residual Method (GMRES)
GMRES iteratively refines the initial solution guess to the
system Ax = b
Householder reflections are used for orthogonalization
Parameters
----------
A : {array, matrix, sparse matrix, LinearOperator}
n x n, linear system to solve
b : {array, matrix}
right hand side, shape is (n,) or (n, 1)
x0 : {array, matrix}
initial guess, default is a vector of zeros
tol : float
relative convergence tolerance, i.e. tol is scaled by the norm
of the initial preconditioned residual
restrt : {None, int}
- if int, restrt is max number of inner iterations
and maxiter is the max number of outer iterations
- if None, do not restart GMRES, and max number of inner iterations
is maxiter
maxiter : {None, int}
- if restrt is None, maxiter is the max number of inner iterations
and GMRES does not restart
- if restrt is int, maxiter is the max number of outer iterations,
and restrt is the max number of inner iterations
xtype : type
dtype for the solution, default is automatic type detection
M : {array, matrix, sparse matrix, LinearOperator}
n x n, inverted preconditioner, i.e. solve M A x = M b.
callback : function
User-supplied function is called after each iteration as
callback( ||rk||_2 ), where rk is the current preconditioned residual
vector
residuals : list
residuals contains the preconditioned residual norm history,
including the initial residual.
Returns
-------
(xNew, info)
xNew : an updated guess to the solution of Ax = b
info : halting status of gmres
== =============================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead. This value
is precisely the order of the Krylov space.
<0 numerical breakdown, or illegal input
== =============================================
Notes
-----
- The LinearOperator class is in scipy.sparse.linalg.interface.
Use this class if you prefer to define A or M as a mat-vec routine
as opposed to explicitly constructing the matrix. A.psolve(..) is
still supported as a legacy.
- For robustness, Householder reflections are used to orthonormalize
the Krylov Space
Givens Rotations are used to provide the residual norm each iteration
Examples
--------
>>> from pyamg.krylov import gmres
>>> from pyamg.util.linalg import norm
>>> import numpy as np
>>> from pyamg.gallery import poisson
>>> A = poisson((10, 10))
>>> b = np.ones((A.shape[0],))
>>> (x, flag) = gmres(A, b, maxiter=2, tol=1e-8, orthog='householder')
>>> print norm(b - A*x)
6.5428213057
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
http://www-users.cs.umn.edu/~saad/books.html
'''
# Convert inputs to linear system, with error checking
A, M, x, b, postprocess = make_system(A, M, x0, b)
dimen = A.shape[0]
# Ensure that warnings are always reissued from this function
import warnings
warnings.filterwarnings('always',
module='pyamg\.krylov\._gmres_householder')
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
if not hasattr(M, 'dtype'):
Mtype = upcast(x.dtype, b.dtype)
else:
Mtype = M.dtype
xtype = upcast(Atype, x.dtype, b.dtype, Mtype)
if restrt is not None:
restrt = int(restrt)
if maxiter is not None:
maxiter = int(maxiter)
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# Set number of outer and inner iterations
if restrt:
if maxiter:
max_outer = maxiter
else:
max_outer = 1
if restrt > dimen:
warn('Setting number of inner iterations (restrt) to maximum \
allowed, which is A.shape[0] ')
restrt = dimen
max_inner = restrt
else:
max_outer = 1
if maxiter > dimen:
warn('Setting number of inner iterations (maxiter) to maximum \
allowed, which is A.shape[0] ')
maxiter = dimen
elif maxiter is None:
maxiter = min(dimen, 40)
max_inner = maxiter
# Get fast access to underlying LAPACK routine
[lartg] = get_lapack_funcs(['lartg'], [x])
# Is this a one dimensional matrix?
if dimen == 1:
entry = ravel(A * array([1.0], dtype=xtype))
return (postprocess(b / entry), 0)
# Prep for method
r = b - ravel(A * x)
# Apply preconditioner
r = ravel(M * r)
normr = norm(r)
if keep_r:
residuals.append(normr)
# Check for nan, inf
# if isnan(r).any() or isinf(r).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol * normb:
if callback is not None:
callback(norm(r))
return (postprocess(x), 0)
# Scale tol by ||r_0||_2, we use the preconditioned residual
# because this is left preconditioned GMRES.
if normr != 0.0:
tol = tol * normr
# Use separate variable to track iterations. If convergence fails, we
# cannot simply report niter = (outer-1)*max_outer + inner. Numerical
# error could cause the inner loop to halt while the actual ||r|| > tol.
niter = 0
# Begin GMRES
for outer in range(max_outer):
# Calculate vector w, which defines the Householder reflector
# Take shortcut in calculating,
# w = r + sign(r[1])*||r||_2*e_1
w = r
beta = mysign(w[0]) * normr
w[0] = w[0] + beta
w[:] = w / norm(w)
# Preallocate for Krylov vectors, Householder reflectors and
# Hessenberg matrix
# Space required is O(dimen*max_inner)
# Givens Rotations
Q = zeros((4 * max_inner, ), dtype=xtype)
# upper Hessenberg matrix (made upper tri with Givens Rotations)
H = zeros((max_inner, max_inner), dtype=xtype)
# Householder reflectors
W = zeros((max_inner + 1, dimen), dtype=xtype)
W[0, :] = w
# Multiply r with (I - 2*w*w.T), i.e. apply the Householder reflector
# This is the RHS vector for the problem in the Krylov Space
g = zeros((dimen, ), dtype=xtype)
g[0] = -beta
for inner in range(max_inner):
# Calculate Krylov vector in two steps
# (1) Calculate v = P_j = (I - 2*w*w.T)v, where k = inner
v = -2.0 * conjugate(w[inner]) * w
v[inner] = v[inner] + 1.0
# (2) Calculate the rest, v = P_1*P_2*P_3...P_{j-1}*ej.
# for j in range(inner-1,-1,-1):
# v -= 2.0*dot(conjugate(W[j,:]), v)*W[j,:]
amg_core.apply_householders(v, ravel(W), dimen, inner - 1, -1, -1)
# Calculate new search direction
v = ravel(A * v)
# Apply preconditioner
v = ravel(M * v)
# Check for nan, inf
# if isnan(v).any() or isinf(v).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Factor in all Householder orthogonal reflections on new search
# direction
# for j in range(inner+1):
# v -= 2.0*dot(conjugate(W[j,:]), v)*W[j,:]
amg_core.apply_householders(v, ravel(W), dimen, 0, inner + 1, 1)
# Calculate next Householder reflector, w
# w = v[inner+1:] + sign(v[inner+1])*||v[inner+1:]||_2*e_{inner+1)
# Note that if max_inner = dimen, then this is unnecessary for the
# last inner iteration, when inner = dimen-1. Here we do not need
# to calculate a Householder reflector or Givens rotation because
# nnz(v) is already the desired length, i.e. we do not need to
# zero anything out.
if inner != dimen - 1:
if inner < (max_inner - 1):
w = W[inner + 1, :]
vslice = v[inner + 1:]
alpha = norm(vslice)
if alpha != 0:
alpha = mysign(vslice[0]) * alpha
# do not need the final reflector for future calculations
if inner < (max_inner - 1):
w[inner + 1:] = vslice
w[inner + 1] += alpha
w[:] = w / norm(w)
# Apply new reflector to v
# v = v - 2.0*w*(w.T*v)
v[inner + 1] = -alpha
v[inner + 2:] = 0.0
if inner > 0:
# Apply all previous Givens Rotations to v
amg_core.apply_givens(Q, v, dimen, inner)
# Calculate the next Givens rotation, where j = inner Note that if
# max_inner = dimen, then this is unnecessary for the last inner
# iteration, when inner = dimen-1. Here we do not need to
# calculate a Householder reflector or Givens rotation because
# nnz(v) is already the desired length, i.e. we do not need to zero
# anything out.
if inner != dimen - 1:
if v[inner + 1] != 0:
[c, s, r] = lartg(v[inner], v[inner + 1])
Qblock = array([[c, s], [-conjugate(s), c]], dtype=xtype)
Q[(inner * 4):((inner + 1) * 4)] = ravel(Qblock).copy()
# Apply Givens Rotation to g, the RHS for the linear system
# in the Krylov Subspace. Note that this dot does a matrix
# multiply, not an actual dot product where a conjugate
# transpose is taken
g[inner:inner + 2] = dot(Qblock, g[inner:inner + 2])
# Apply effect of Givens Rotation to v
v[inner] = dot(Qblock[0, :], v[inner:inner + 2])
v[inner + 1] = 0.0
# Write to upper Hessenberg Matrix,
# the LHS for the linear system in the Krylov Subspace
H[:, inner] = v[0:max_inner]
niter += 1
# Don't update normr if last inner iteration, because
# normr is calculated directly after this loop ends.
if inner < max_inner - 1:
normr = abs(g[inner + 1])
if normr < tol:
break
# Allow user access to residual
if callback is not None:
callback(normr)
if keep_r:
residuals.append(normr)
# end inner loop, back to outer loop
# Find best update to x in Krylov Space, V. Solve inner+1 x inner+1
# system. Apparently this is the best way to solve a triangular system
# in the magical world of scipy
# piv = arange(inner+1)
# y = lu_solve((H[0:(inner+1), 0:(inner+1)], piv), g[0:(inner+1)],
# trans=0)
y = sp.linalg.solve(H[0:(inner + 1), 0:(inner + 1)], g[0:(inner + 1)])
# Use Horner like Scheme to map solution, y, back to original space.
# Note that we do not use the last reflector.
update = zeros(x.shape, dtype=xtype)
# for j in range(inner,-1,-1):
# update[j] += y[j]
# # Apply j-th reflector, (I - 2.0*w_j*w_j.T)*upadate
# update -= 2.0*dot(conjugate(W[j,:]), update)*W[j,:]
amg_core.householder_hornerscheme(update, ravel(W), ravel(y), dimen,
inner, -1, -1)
x[:] = x + update
r = b - ravel(A * x)
# Apply preconditioner
r = ravel(M * r)
normr = norm(r)
# Check for nan, inf
# if isnan(r).any() or isinf(r).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Allow user access to residual
if callback is not None:
callback(normr)
if keep_r:
residuals.append(normr)
# Has GMRES stagnated?
indices = (x != 0)
if indices.any():
change = max(abs(update[indices] / x[indices]))
if change < 1e-12:
# No change, halt
return (postprocess(x), -1)
# test for convergence
if normr < tol:
return (postprocess(x), 0)
# end outer loop
return (postprocess(x), niter)
def gmres_mgs(A, b, x0=None, tol=1e-5, restrt=None, maxiter=None, xtype=None,
M=None, callback=None, residuals=None, reorth=False):
'''
Generalized Minimum Residual Method (GMRES)
GMRES iteratively refines the initial solution guess to the system
Ax = b
Modified Gram-Schmidt version
Parameters
----------
A : {array, matrix, sparse matrix, LinearOperator}
n x n, linear system to solve
b : {array, matrix}
right hand side, shape is (n,) or (n,1)
x0 : {array, matrix}
initial guess, default is a vector of zeros
tol : float
relative convergence tolerance, i.e. tol is scaled by the norm
of the initial preconditioned residual
restrt : {None, int}
- if int, restrt is max number of inner iterations
and maxiter is the max number of outer iterations
- if None, do not restart GMRES, and max number of inner iterations
is maxiter
maxiter : {None, int}
- if restrt is None, maxiter is the max number of inner iterations
and GMRES does not restart
- if restrt is int, maxiter is the max number of outer iterations,
and restrt is the max number of inner iterations
xtype : type
dtype for the solution, default is automatic type detection
M : {array, matrix, sparse matrix, LinearOperator}
n x n, inverted preconditioner, i.e. solve M A x = M b.
callback : function
User-supplied function is called after each iteration as
callback( ||rk||_2 ), where rk is the current preconditioned residual
vector
residuals : list
residuals contains the preconditioned residual norm history,
including the initial residual.
reorth : boolean
If True, then a check is made whether to re-orthogonalize the Krylov
space each GMRES iteration
Returns
-------
(xNew, info)
xNew : an updated guess to the solution of Ax = b
info : halting status of gmres
== =============================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead. This value
is precisely the order of the Krylov space.
<0 numerical breakdown, or illegal input
== =============================================
Notes
-----
- The LinearOperator class is in scipy.sparse.linalg.interface.
Use this class if you prefer to define A or M as a mat-vec routine
as opposed to explicitly constructing the matrix. A.psolve(..) is
still supported as a legacy.
- For robustness, modified Gram-Schmidt is used to orthogonalize the
Krylov Space Givens Rotations are used to provide the residual norm
each iteration
Examples
--------
>>> from pyamg.krylov import gmres
>>> from pyamg.util.linalg import norm
>>> import numpy as np
>>> from pyamg.gallery import poisson
>>> A = poisson((10,10))
>>> b = np.ones((A.shape[0],))
>>> (x,flag) = gmres(A,b, maxiter=2, tol=1e-8, orthog='mgs')
>>> print norm(b - A*x)
>>> 6.5428213057
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
http://www-users.cs.umn.edu/~saad/books.html
.. [2] C. T. Kelley, http://www4.ncsu.edu/~ctk/matlab_roots.html
'''
# Convert inputs to linear system, with error checking
A, M, x, b, postprocess = make_system(A, M, x0, b)
dimen = A.shape[0]
# Ensure that warnings are always reissued from this function
import warnings
warnings.filterwarnings('always', module='pyamg\.krylov\._gmres_mgs')
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
if not hasattr(M, 'dtype'):
Mtype = upcast(x.dtype, b.dtype)
else:
Mtype = M.dtype
xtype = upcast(Atype, x.dtype, b.dtype, Mtype)
if restrt is not None:
restrt = int(restrt)
if maxiter is not None:
maxiter = int(maxiter)
# Get fast access to underlying BLAS routines
# dotc is the conjugate dot, dotu does no conjugation
[lartg] = get_lapack_funcs(['lartg'], [x] )
if iscomplexobj(zeros((1,), dtype=xtype)):
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dotu', 'dotc', 'scal'], [x])
else:
# real type
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dot', 'dot', 'scal'], [x])
# Make full use of direct access to BLAS by defining own norm
def norm(z):
return sqrt(real(dotc(z, z)))
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# Set number of outer and inner iterations
if restrt:
if maxiter:
max_outer = maxiter
else:
max_outer = 1
if restrt > dimen:
warn('Setting number of inner iterations (restrt) to maximum\
allowed, which is A.shape[0] ')
restrt = dimen
max_inner = restrt
else:
max_outer = 1
if maxiter > dimen:
warn('Setting number of inner iterations (maxiter) to maximum\
allowed, which is A.shape[0] ')
maxiter = dimen
elif maxiter is None:
maxiter = min(dimen, 40)
max_inner = maxiter
# Is this a one dimensional matrix?
if dimen == 1:
entry = ravel(A*array([1.0], dtype=xtype))
return (postprocess(b/entry), 0)
# Prep for method
r = b - ravel(A*x)
# Apply preconditioner
r = ravel(M*r)
normr = norm(r)
if keep_r:
residuals.append(normr)
# Check for nan, inf
# if isnan(r).any() or isinf(r).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol*normb:
if callback is not None:
callback(norm(r))
return (postprocess(x), 0)
# Scale tol by ||r_0||_2, we use the preconditioned residual
# because this is left preconditioned GMRES.
if normr != 0.0:
tol = tol*normr
# Use separate variable to track iterations. If convergence fails, we
# cannot simply report niter = (outer-1)*max_outer + inner. Numerical
# error could cause the inner loop to halt while the actual ||r|| > tol.
niter = 0
# Begin GMRES
for outer in range(max_outer):
# Preallocate for Givens Rotations, Hessenberg matrix and Krylov Space
# Space required is O(dimen*max_inner).
# NOTE: We are dealing with row-major matrices, so we traverse in a
# row-major fashion,
# i.e., H and V's transpose is what we store.
Q = [] # Givens Rotations
# Upper Hessenberg matrix, which is then
# converted to upper tri with Givens Rots
H = zeros((max_inner+1, max_inner+1), dtype=xtype)
V = zeros((max_inner+1, dimen), dtype=xtype) # Krylov Space
# vs store the pointers to each column of V.
# This saves a considerable amount of time.
vs = []
# v = r/normr
V[0, :] = scal(1.0/normr, r)
vs.append(V[0, :])
# This is the RHS vector for the problem in the Krylov Space
g = zeros((dimen,), dtype=xtype)
g[0] = normr
for inner in range(max_inner):
# New Search Direction
v = V[inner+1, :]
v[:] = ravel(M*(A*vs[-1]))
vs.append(v)
normv_old = norm(v)
# Check for nan, inf
# if isnan(V[inner+1, :]).any() or isinf(V[inner+1, :]).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Modified Gram Schmidt
for k in range(inner+1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = alpha
v[:] = axpy(vk, v, dimen, -alpha)
normv = norm(v)
H[inner, inner+1] = normv
# Re-orthogonalize
if (reorth is True) and (normv_old == normv_old + 0.001*normv):
for k in range(inner+1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = H[inner, k] + alpha
v[:] = axpy(vk, v, dimen, -alpha)
# Check for breakdown
if H[inner, inner+1] != 0.0:
v[:] = scal(1.0/H[inner, inner+1], v)
# Apply previous Givens rotations to H
if inner > 0:
apply_givens(Q, H[inner, :], inner)
# Calculate and apply next complex-valued Givens Rotation
# ==> Note that if max_inner = dimen, then this is unnecessary
# for the last inner
# iteration, when inner = dimen-1.
if inner != dimen-1:
if H[inner, inner+1] != 0:
[c, s, r] = lartg(H[inner, inner], H[inner, inner+1])
Qblock = array([[c, s], [-conjugate(s), c]], dtype=xtype)
Q.append(Qblock)
# Apply Givens Rotation to g,
# the RHS for the linear system in the Krylov Subspace.
g[inner:inner+2] = sp.dot(Qblock, g[inner:inner+2])
# Apply effect of Givens Rotation to H
H[inner, inner] = dotu(Qblock[0, :],
H[inner, inner:inner+2])
H[inner, inner+1] = 0.0
niter += 1
# Don't update normr if last inner iteration, because
# normr is calculated directly after this loop ends.
if inner < max_inner-1:
normr = abs(g[inner+1])
if normr < tol:
break
# Allow user access to residual
if callback is not None:
callback(normr)
if keep_r:
residuals.append(normr)
# end inner loop, back to outer loop
# Find best update to x in Krylov Space V. Solve inner x inner system.
y = sp.linalg.solve(H[0:inner+1, 0:inner+1].T, g[0:inner+1])
update = ravel(sp.mat(V[:inner+1, :]).T*y.reshape(-1, 1))
x = x + update
r = b - ravel(A*x)
# Apply preconditioner
r = ravel(M*r)
normr = norm(r)
# Check for nan, inf
# if isnan(r).any() or isinf(r).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Allow user access to residual
if callback is not None:
callback(normr)
if keep_r:
residuals.append(normr)
# Has GMRES stagnated?
indices = (x != 0)
if indices.any():
change = max(abs(update[indices] / x[indices]))
if change < 1e-12:
# No change, halt
return (postprocess(x), -1)
# test for convergence
if normr < tol:
return (postprocess(x), 0)
# end outer loop
return (postprocess(x), niter)
def gmres_mgs(surf_array, field_array, X, b, param, ind0, timing, kernel):
"""
GMRES solver.
Arguments
----------
surf_array : array, contains the surface classes of each region on the
surface.
field_array: array, contains the Field classes of each region on the surface.
X : array, initial guess.
b : array, right hand side.
param : class, parameters related to the surface.
ind0 : class, it contains the indices related to the treecode
computation.
timing : class, it contains timing information for different parts of
the code.
kernel : pycuda source module.
Returns
--------
X : array, an updated guess to the solution.
iteration : int, number of outer iterations for convergence
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
http://www-users.cs.umn.edu/~saad/books.html
.. [2] C. T. Kelley, http://www4.ncsu.edu/~ctk/matlab_roots.html
"""
# Defining xtype as dtype of the problem, to decide which BLAS functions
# import.
xtype = upcast(X.dtype, b.dtype)
# Get fast access to underlying BLAS routines
# dotc is the conjugate dot, dotu does no conjugation
[lartg] = get_lapack_funcs(['lartg'], [X])
if numpy.iscomplexobj(numpy.zeros((1, ), dtype=xtype)):
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dotu', 'dotc', 'scal'], [X])
else:
# real type
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dot', 'dot', 'scal'], [X])
# Make full use of direct access to BLAS by defining own norm
def norm(z):
return numpy.sqrt(numpy.real(dotc(z, z)))
# Defining dimension
dimen = len(X)
max_iter = param.max_iter
R = param.restart
tol = param.tol
# Set number of outer and inner iterations
if R > dimen:
warn('Setting number of inner iterations (restrt) to maximum\
allowed, which is A.shape[0] ')
R = dimen
max_inner = R
#max_outer should be max_iter/max_inner but this might not be an integer
#so we get the ceil of the division.
#In the inner loop there is a if statement to break in case max_iter is
#reached.
max_outer = int(numpy.ceil(max_iter / max_inner))
# Prep for method
aux = gmres_dot(X, surf_array, field_array, ind0, param, timing, kernel)
r = b - aux
normr = norm(r)
# Check initial guess ( scaling by b, if b != 0, must account for
# case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol * normb:
return X, 0
iteration = 0
# Here start the GMRES
for outer in range(max_outer):
# Preallocate for Givens Rotations, Hessenberg matrix and Krylov Space
# Space required is O(dimen*max_inner).
# NOTE: We are dealing with row-major matrices, so we traverse in a
# row-major fashion,
# i.e., H and V's transpose is what we store.
Q = [] # Initialzing Givens Rotations
# Upper Hessenberg matrix, which is then
# converted to upper triagonal with Givens Rotations
H = numpy.zeros((max_inner + 1, max_inner + 1), dtype=xtype)
V = numpy.zeros((max_inner + 1, dimen), dtype=xtype) # Krylov space
# vs store the pointers to each column of V.
# This saves a considerable amount of time.
vs = []
# v = r/normr
V[0, :] = scal(1.0 / normr, r) # scal wrapper of dscal --> x = a*x
vs.append(V[0, :])
#Saving initial residual to be used to calculate the rel_resid
if iteration == 0:
res_0 = normb
#RHS vector in the Krylov space
g = numpy.zeros((dimen, ), dtype=xtype)
g[0] = normr
for inner in range(max_inner):
#New search direction
v = V[inner + 1, :]
v[:] = gmres_dot(vs[-1], surf_array, field_array, ind0, param,
timing, kernel)
vs.append(v)
#Modified Gram Schmidt
for k in range(inner + 1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = alpha
v[:] = axpy(vk, v, dimen, -alpha) # y := a*x + y
#axpy is a wrapper for daxpy (blas function)
normv = norm(v)
H[inner, inner + 1] = normv
#Check for breakdown
if H[inner, inner + 1] != 0.0:
v[:] = scal(1.0 / H[inner, inner + 1], v)
#Apply for Givens rotations to H
if inner > 0:
apply_givens(Q, H[inner, :], inner)
#Calculate and apply next complex-valued Givens rotations
#If max_inner = dimen, we don't need to calculate, this
#is unnecessary for the last inner iteration when inner = dimen -1
if inner != dimen - 1:
if H[inner, inner + 1] != 0:
#lartg is a lapack function that computes the parameters
#for a Givens rotation
[c, s, _] = lartg(H[inner, inner], H[inner, inner + 1])
Qblock = numpy.array([[c, s], [-numpy.conjugate(s), c]],
dtype=xtype)
Q.append(Qblock)
#Apply Givens Rotations to RHS for the linear system in
# the krylov space.
g[inner:inner + 2] = scipy.dot(Qblock, g[inner:inner + 2])
#Apply Givens rotations to H
H[inner, inner] = dotu(Qblock[0, :], H[inner,
inner:inner + 2])
H[inner, inner + 1] = 0.0
iteration += 1
if inner < max_inner - 1:
normr = abs(g[inner + 1])
rel_resid = normr / res_0
if rel_resid < tol:
break
if iteration % 1 == 0:
print('Iteration: {}, relative residual: {}'.format(
iteration, rel_resid))
if (inner + 1 == R):
print('Residual: {}. Restart...'.format(rel_resid))
if iteration == max_iter:
print(
'Warning!!!!'
'You have reached the maximum number of iterations : {}.'.
format(iteration))
print(
'The run will stop. Check the residual behaviour you might have a bug.'
'For future runs you might consider changing the tolerance or'
' increasing the number of max_iter.')
break
# end inner loop, back to outer loop
# Find best update to X in Krylov Space V. Solve inner X inner system.
y = scipy.linalg.solve(H[0:inner + 1, 0:inner + 1].T, g[0:inner + 1])
update = numpy.ravel(scipy.mat(V[:inner + 1, :]).T * y.reshape(-1, 1))
X = X + update
aux = gmres_dot(X, surf_array, field_array, ind0, param, timing,
kernel)
r = b - aux
normr = norm(r)
rel_resid = normr / res_0
# test for convergence
if rel_resid < tol:
print('GMRES solve')
print('Converged after {} iterations to a residual of {}'.format(
iteration, rel_resid))
print('Time weight vector: {}'.format(timing.time_mass))
print('Time sort : {}'.format(timing.time_sort))
print('Time data transfer: {}'.format(timing.time_trans))
print('Time P2M : {}'.format(timing.time_P2M))
print('Time M2M : {}'.format(timing.time_M2M))
print('Time M2P : {}'.format(timing.time_M2P))
print('Time P2P : {}'.format(timing.time_P2P))
print('\tTime analy: {}'.format(timing.time_an))
return X, iteration
#end outer loop
return X, iteration
def test_upcast(self):
assert_equal(sputils.upcast("intc"), np.intc)
assert_equal(sputils.upcast("int32", "float32"), np.float64)
assert_equal(sputils.upcast("bool", complex, float), np.complex128)
assert_equal(sputils.upcast("i", "d"), np.float64)
def jfnk(fluxName,
b,
U,
Dt,
Dx,
x0=None,
Uref=1.,
tol=1e-5,
restrt=None,
maxiter=None,
xtype=None,
M=None,
callback=None,
residuals=None):
'''
Jacobian free Newton-Krylov method :
For robustness, Householder reflections are used to orthonormalize the Krylov Space
Givens Rotations are used to provide the residual norm each iteration
Parameters
----------
fluxName : string
name of the flux to use to compute the jacobian product
b : array
n x 1, right hand side
U : array
n x 1, right hand side
Dt : integer
time step for the approximation of the jacobian product
x0 : array
n x 1, initial guess
default is a vector of zeros
tol : float
convergence tolerance
restrt : int
number of restarts
total iterations = restrt*maxiter
maxiter : int
maximum number of allowed inner iterations
xtype : type
dtype for the solution
M : matrix-like
n x n, inverted preconditioner, i.e. solve M A x = b.
For preconditioning with a mat-vec routine, set
A.psolve = func, where func := M y
callback : function
callback( ||resid||_2 ) is called each iteration,
residuals : {None, empty-list}
If empty-list, residuals holds the residual norm history,
including the initial residual, upon completion
Returns
-------
xNew -- an updated guess to the solution of Ax = b
References
----------
Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
'''
dimen = b.shape[0]
# Choose type
xtype = upcast(b.dtype)
# We assume henceforth that shape=(n,) for all arrays
b = ravel(array(b, xtype))
x = ravel(array(x0, xtype))
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# check number of iterations
if restrt == None:
restrt = 1
elif restrt < 1:
raise ValueError('Number of restarts must be positive')
if maxiter == None:
maxiter = int(max(ceil(dimen / restrt)))
elif maxiter < 1:
raise ValueError('Number of iterations must be positive')
elif maxiter > dimen:
warn(
'maximimum allowed inner iterations (maxiter) are the number of degress of freedom'
)
maxiter = dimen
# Scale tol by normb
normb = linalg.norm(b)
if normb == 0:
pass
else:
tol = tol * normb
# Prep for method
r = b - ravel(jacobianProduct(fluxName, U, x, Dt, Dx, Uref))
normr = linalg.norm(r)
if keep_r:
residuals.append(normr)
# Is initial guess sufficient?
if normr <= tol:
if callback != None:
callback(norm(r))
return x
# Use separate variable to track iterations. If convergence fails, we cannot
# simply report niter = (outer-1)*maxiter + inner. Numerical error could cause
# the inner loop to halt before reaching maxiter while the actual ||r|| > tol.
niter = 0
# Begin GMRES
for outer in range(restrt):
# Calculate vector w, which defines the Householder reflector
# Take shortcut in calculating,
# w = r + sign(r[1])*||r||_2*e_1
w = r
beta = mysign(w[0]) * normr
w[0] += beta
w = w / linalg.norm(w)
# Preallocate for Krylov vectors, Householder reflectors and Hessenberg matrix
# Space required is O(dimen*maxiter)
H = zeros(
(maxiter, maxiter), dtype=xtype
) # upper Hessenberg matrix (actually made upper tri with Given's Rotations)
W = zeros((dimen, maxiter), dtype=xtype) # Householder reflectors
W[:, 0] = w
# Multiply r with (I - 2*w*w.T), i.e. apply the Householder reflector
# This is the RHS vector for the problem in the Krylov Space
g = zeros((dimen, ), dtype=xtype)
g[0] = -beta
for inner in range(maxiter):
# Calcute Krylov vector in two steps
# (1) Calculate v = P_j = (I - 2*w*w.T)v, where k = inner
v = -2.0 * conjugate(w[inner]) * w
v[inner] += 1.0
# (2) Calculate the rest, v = P_1*P_2*P_3...P_{j-1}*ej.
for j in range(inner - 1, -1, -1):
v = v - 2.0 * dot(conjugate(W[:, j]), v) * W[:, j]
# Calculate new search direction (A*v)
v = ravel(jacobianProduct(fluxName, U, v, Dt, Dx, Uref))
# Factor in all Householder orthogonal reflections on new search direction
for j in range(inner + 1):
v = v - 2.0 * dot(conjugate(W[:, j]), v) * W[:, j]
# Calculate next Householder reflector, w
# w = v[inner+1:] + sign(v[inner+1])*||v[inner+1:]||_2*e_{inner+1)
# Note that if maxiter = dimen, then this is unnecessary for the last inner
# iteration, when inner = dimen-1. Here we do not need to calculate a
# Householder reflector or Given's rotation because nnz(v) is already the
# desired length, i.e. we do not need to zero anything out.
if inner != dimen - 1:
w = zeros((dimen, ), dtype=xtype)
vslice = v[inner + 1:]
alpha = linalg.norm(vslice)
if alpha != 0:
alpha = mysign(vslice[0]) * alpha
# We do not need the final reflector for future calculations
if inner < (maxiter - 1):
w[inner + 1:] = vslice
w[inner + 1] += alpha
w = w / linalg.norm(w)
W[:, inner + 1] = w
# Apply new reflector to v
# v = v - 2.0*w*(w.T*v)
v[inner + 1] = -alpha
v[inner + 2:] = 0.0
# Apply all previous Given's Rotations to v
if inner == 0:
# Q will store the cumulative effect of all Given's Rotations
Q = scipy.sparse.eye(dimen, dimen, format='csr', dtype=xtype)
# Declare initial Qj, which will be the current Given's Rotation
rowptr = hstack((array([0, 2, 4],
int), arange(5, dimen + 3, dtype=int)))
colindices = hstack((array([0, 1, 0, 1],
int), arange(2, dimen, dtype=int)))
data = ones((dimen + 2, ), dtype=xtype)
Qj = csr_matrix((data, colindices, rowptr),
shape=(dimen, dimen),
dtype=xtype)
else:
# Could avoid building a global Given's Rotation, by storing
# and applying each 2x2 matrix individually.
# But that would require looping, the bane of wonderful Python
Q = Qj * Q
v = Q * v
# Calculate Qj, the next Given's rotation, where j = inner
# Note that if maxiter = dimen, then this is unnecessary for the last inner
# iteration, when inner = dimen-1. Here we do not need to calculate a
# Householder reflector or Given's rotation because nnz(v) is already the
# desired length, i.e. we do not need to zero anything out.
if inner != dimen - 1:
if v[inner + 1] != 0:
# Calculate terms for complex 2x2 Given's Rotation
# Note that abs(x) takes the complex modulus
h1 = v[inner]
h2 = v[inner + 1]
h1_mag = abs(h1)
h2_mag = abs(h2)
if h1_mag < h2_mag:
mu = h1 / h2
tau = conjugate(mu) / abs(mu)
else:
mu = h2 / h1
tau = mu / abs(mu)
denom = sqrt(h1_mag**2 + h2_mag**2)
c = h1_mag / denom
s = h2_mag * tau / denom
Qblock = array([[c, conjugate(s)], [-s, c]], dtype=xtype)
# Modify Qj in csr-format so that it represents the current
# global Given's Rotation equivalent to Qblock
if inner != 0:
Qj.data[inner - 1] = 1.0
Qj.indices[inner - 1] = inner - 1
Qj.indptr[inner - 1] = inner - 1
Qj.data[inner:inner + 4] = ravel(Qblock)
Qj.indices[inner:inner +
4] = [inner, inner + 1, inner, inner + 1]
Qj.indptr[inner:inner + 3] = [inner, inner + 2, inner + 4]
# Apply Given's Rotation to g,
# the RHS for the linear system in the Krylov Subspace.
# Note that this dot does a matrix multiply, not an actual
# dot product where a conjugate transpose is taken
g[inner:inner + 2] = dot(Qblock, g[inner:inner + 2])
# Apply effect of Given's Rotation to v
v[inner] = dot(Qblock[0, :], v[inner:inner + 2])
v[inner + 1] = 0.0
# Write to upper Hessenberg Matrix,
# the LHS for the linear system in the Krylov Subspace
H[:, inner] = v[0:maxiter]
# Don't update normr if last inner iteration, because
# normr is calculated directly after this loop ends.
if inner < maxiter - 1:
normr = abs(g[inner + 1])
if normr < tol:
break
# Allow user access to residual
if callback != None:
callback(normr)
if keep_r:
residuals.append(normr)
niter += 1
# end inner loop, back to outer loop
# Find best update to x in Krylov Space, V. Solve inner+1 x inner+1 system.
# Apparently this is the best way to solve a triangular
# system in the magical world of scipy
piv = arange(inner + 1)
y = lu_solve((H[0:(inner + 1), 0:(inner + 1)], piv),
g[0:(inner + 1)],
trans=0)
# Use Horner like Scheme to map solution, y, back to original space.
# Note that we do not use the last reflector.
update = zeros(x.shape, dtype=xtype)
for j in range(inner, -1, -1):
update[j] += y[j]
# Apply j-th reflector, (I - 2.0*w_j*w_j.T)*upadate
update = update - 2.0 * dot(conjugate(W[:, j]), update) * W[:, j]
x = x + update
r = b - ravel(jacobianProduct(fluxName, U, x, Dt, Dx, Uref))
# Allow user access to residual
if callback != None:
callback(normr)
if keep_r:
residuals.append(normr)
# Has GMRES stagnated?
indices = (x != 0)
if indices.any():
change = max(abs(update[indices] / x[indices]))
if change < 1e-12:
# No change, halt
return x
# test for convergence
if normr < tol:
return x
# end outer loop
return x
def gmres_mgs(surf_array, field_array, X, b, param, ind0, timing, kernel):
"""
GMRES solver.
Arguments
----------
surf_array : array, contains the surface classes of each region on the
surface.
field_array: array, contains the Field classes of each region on the surface.
X : array, initial guess.
b : array, right hand side.
param : class, parameters related to the surface.
ind0 : class, it contains the indices related to the treecode
computation.
timing : class, it contains timing information for different parts of
the code.
kernel : pycuda source module.
Returns
--------
X : array, an updated guess to the solution.
iteration : int, number of outer iterations for convergence
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
http://www-users.cs.umn.edu/~saad/books.html
.. [2] C. T. Kelley, http://www4.ncsu.edu/~ctk/matlab_roots.html
"""
# Defining xtype as dtype of the problem, to decide which BLAS functions
# import.
xtype = upcast(X.dtype, b.dtype)
# Get fast access to underlying BLAS routines
# dotc is the conjugate dot, dotu does no conjugation
[lartg] = get_lapack_funcs(['lartg'], [X] )
if numpy.iscomplexobj(numpy.zeros((1,), dtype=xtype)):
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dotu', 'dotc', 'scal'], [X])
else:
# real type
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dot', 'dot', 'scal'], [X])
# Make full use of direct access to BLAS by defining own norm
def norm(z):
return numpy.sqrt(numpy.real(dotc(z, z)))
# Defining dimension
dimen = len(X)
max_iter = param.max_iter
R = param.restart
tol = param.tol
# Set number of outer and inner iterations
if R > dimen:
warn('Setting number of inner iterations (restrt) to maximum\
allowed, which is A.shape[0] ')
R = dimen
max_inner = R
#max_outer should be max_iter/max_inner but this might not be an integer
#so we get the ceil of the division.
#In the inner loop there is a if statement to break in case max_iter is
#reached.
max_outer = int(numpy.ceil(max_iter/max_inner))
# Prep for method
aux = gmres_dot(X, surf_array, field_array, ind0, param, timing, kernel)
r = b - aux
normr = norm(r)
# Check initial guess ( scaling by b, if b != 0, must account for
# case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol*normb:
return X
iteration = 0
# Here start the GMRES
for outer in range(max_outer):
# Preallocate for Givens Rotations, Hessenberg matrix and Krylov Space
# Space required is O(dimen*max_inner).
# NOTE: We are dealing with row-major matrices, so we traverse in a
# row-major fashion,
# i.e., H and V's transpose is what we store.
Q = [] # Initialzing Givens Rotations
# Upper Hessenberg matrix, which is then
# converted to upper triagonal with Givens Rotations
H = numpy.zeros((max_inner+1, max_inner+1), dtype=xtype)
V = numpy.zeros((max_inner+1, dimen), dtype=xtype) # Krylov space
# vs store the pointers to each column of V.
# This saves a considerable amount of time.
vs = []
# v = r/normr
V[0, :] = scal(1.0/normr, r) # scal wrapper of dscal --> x = a*x
vs.append(V[0, :])
#Saving initial residual to be used to calculate the rel_resid
if iteration==0:
res_0 = normb
#RHS vector in the Krylov space
g = numpy.zeros((dimen, ), dtype=xtype)
g[0] = normr
for inner in range(max_inner):
#New search direction
v= V[inner+1, :]
v[:] = gmres_dot(vs[-1], surf_array, field_array, ind0, param,
timing, kernel)
vs.append(v)
#Modified Gram Schmidt
for k in range(inner+1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = alpha
v[:] = axpy(vk, v, dimen, -alpha) # y := a*x + y
#axpy is a wrapper for daxpy (blas function)
normv = norm(v)
H[inner, inner+1] = normv
#Check for breakdown
if H[inner, inner+1] != 0.0:
v[:] = scal(1.0/H[inner, inner+1], v)
#Apply for Givens rotations to H
if inner > 0:
apply_givens(Q, H[inner, :], inner)
#Calculate and apply next complex-valued Givens rotations
#If max_inner = dimen, we don't need to calculate, this
#is unnecessary for the last inner iteration when inner = dimen -1
if inner != dimen - 1:
if H[inner, inner+1] != 0:
#lartg is a lapack function that computes the parameters
#for a Givens rotation
[c, s, _] = lartg(H[inner, inner], H[inner, inner+1])
Qblock = numpy.array([[c, s], [-numpy.conjugate(s),c]], dtype=xtype)
Q.append(Qblock)
#Apply Givens Rotations to RHS for the linear system in
# the krylov space.
g[inner:inner+2] = scipy.dot(Qblock, g[inner:inner+2])
#Apply Givens rotations to H
H[inner, inner] = dotu(Qblock[0,:], H[inner, inner:inner+2])
H[inner, inner+1] = 0.0
iteration+= 1
if inner < max_inner-1:
normr = abs(g[inner+1])
rel_resid = normr/res_0
if rel_resid < tol:
break
if iteration%1==0:
print('Iteration: {}, relative residual: {}'.format(iteration,rel_resid))
if (inner + 1 == R):
print('Residual: {}. Restart...'.format(rel_resid))
if iteration==max_iter:
print('Warning!!!!'
'You have reached the maximum number of iterations : {}.'.format(iteration))
print('The run will stop. Check the residual behaviour you might have a bug.'
'For future runs you might consider changing the tolerance or'
' increasing the number of max_iter.')
break
# end inner loop, back to outer loop
# Find best update to X in Krylov Space V. Solve inner X inner system.
y = scipy.linalg.solve (H[0:inner+1, 0:inner+1].T, g[0:inner+1])
update = numpy.ravel(scipy.mat(V[:inner+1, :]).T * y.reshape(-1,1))
X= X + update
aux = gmres_dot(X, surf_array, field_array, ind0, param, timing, kernel)
r = b - aux
normr = norm(r)
rel_resid = normr/res_0
# test for convergence
if rel_resid < tol:
print('GMRES solve')
print('Converged after {} iterations to a residual of {}'.format(iteration,rel_resid))
print('Time weight vector: {}'.format(timing.time_mass))
print('Time sort : {}'.format(timing.time_sort))
print('Time data transfer: {}'.format(timing.time_trans))
print('Time P2M : {}'.format(timing.time_P2M))
print('Time M2M : {}'.format(timing.time_M2M))
print('Time M2P : {}'.format(timing.time_M2P))
print('Time P2P : {}'.format(timing.time_P2P))
print('\tTime analy: {}'.format(timing.time_an))
return X, iteration
#end outer loop
return X, iteration
def solve(self, b, x0=None, tol=1e-5, maxiter=100, cycle='V', accel=None,
callback=None, residuals=None, return_residuals=False, additive=False):
if self.num_hierarchies == 0:
raise ValueError("Cannot solve - zero hierarchies stored.")
from pyamg.util.linalg import residual_norm, norm
if x0 is None:
x = np.zeros_like(b)
else:
x = np.array(x0) # copy
cycle = str(cycle).upper()
# AMLI cycles require hermitian matrix
if (cycle == 'AMLI') and hasattr(self.levels[0].A, 'symmetry'):
if self.levels[0].A.symmetry != 'hermitian':
raise ValueError('AMLI cycles require \
symmetry to be hermitian')
# Create uniform types for A, x and b
# Clearly, this logic doesn't handle the case of real A and complex b
from scipy.sparse.sputils import upcast
from pyamg.util.utils import to_type
A = self.hierarchy_set[0].levels[0].A
tp = upcast(b.dtype, x.dtype, A.dtype)
[b, x] = to_type(tp, [b, x])
b = np.ravel(b)
x = np.ravel(x)
if accel is not None:
# Check for AMLI compatability
if (accel != 'fgmres') and (cycle == 'AMLI'):
raise ValueError('AMLI cycles require acceleration (accel) \
to be fgmres, or no acceleration')
# Acceleration is being used
if isinstance(accel, basestring):
from pyamg import krylov
from scipy.sparse.linalg import isolve
if hasattr(krylov, accel):
accel = getattr(krylov, accel)
else:
accel = getattr(isolve, accel)
M = self.aspreconditioner(cycle=cycle)
n = x.shape[0]
try: # try PyAMG style interface which has a residuals parameter
return accel(A, b, x0=x0, tol=tol, maxiter=maxiter, M=M,
callback=callback, residuals=residuals)[0].reshape((n,1))
except:
# try the scipy.sparse.linalg.isolve style interface,
# which requires a call back function if a residual
# history is desired
cb = callback
if residuals is not None:
residuals[:] = [residual_norm(A, x, b)]
def callback(x):
if sp.isscalar(x):
residuals.append(x)
else:
residuals.append(residual_norm(A, x, b))
if cb is not None:
cb(x)
return accel(A, b, x0=x0, tol=tol, maxiter=maxiter, M=M,
callback=callback)[0].reshape((n,1))
else:
# Scale tol by normb
# Don't scale tol earlier. The accel routine should also scale tol
normb = norm(b)
if normb != 0:
tol = tol * normb
if return_residuals:
warn('return_residuals is deprecated. Use residuals instead')
residuals = []
if residuals is None:
residuals = []
else:
residuals[:] = []
residuals.append(residual_norm(A, x, b))
iter_num = 0
while iter_num < maxiter and residuals[-1] > tol:
# ----------- Additive solve ----------- #
# ------ This doesn't really work ------ #
if additive:
x_copy = deepcopy(x)
for hierarchy in self.hierarchy_set:
this_x = deepcopy(x_copy)
if len(hierarchy.levels) == 1:
this_x = hierarchy.coarse_solver(A, b)
else:
temp = hierarchy.test_solve(0, this_x, b, cycle)
x += temp
# ----------- Normal solve ----------- #
else:
# One solve for each hierarchy in set
for hierarchy in self.hierarchy_set:
# hierarchy has only 1 level
if len(hierarchy.levels) == 1:
x = hierarchy.coarse_solver(A, b)
else:
hierarchy.test_solve(0, x, b, cycle)
residuals.append(residual_norm(A, x, b))
iter_num += 1
if callback is not None:
callback(x)
n = x.shape[0]
if return_residuals:
return x.reshape((n,1)), residuals
else:
return x.reshape((n,1))
def gmres_mgs(surf_array, field_array, X, b, param, ind0, timing, kernel):
"""
GMRES solver.
Arguments
----------
surf_array : array, contains the surface classes of each region on the
surface.
field_array: array, contains the Field classes of each region on the surface.
X : array, initial guess.
b : array, right hand side.
param : class, parameters related to the surface.
ind0 : class, it contains the indices related to the treecode
computation.
timing : class, it contains timing information for different parts of
the code.
kernel : pycuda source module.
Returns
--------
X : array, an updated guess to the solution.
"""
output_path = os.path.join(
os.environ.get('PYGBE_PROBLEM_FOLDER'), 'OUTPUT')
#Defining xtype as dtype of the problem, to decide which BLAS functions
#import.
xtype = upcast(X.dtype, b.dtype)
# Get fast access to underlying BLAS routines
# dotc is the conjugate dot, dotu does no conjugation
if numpy.iscomplexobj(numpy.zeros((1,), dtype=xtype)):
[axpy, dotu, dotc, scal, rotg] =\
get_blas_funcs(['axpy', 'dotu', 'dotc', 'scal', 'rotg'], [X])
else:
# real type
[axpy, dotu, dotc, scal, rotg] =\
get_blas_funcs(['axpy', 'dot', 'dot', 'scal', 'rotg'], [X])
# Make full use of direct access to BLAS by defining own norm
def norm(z):
return numpy.sqrt(numpy.real(dotc(z, z)))
#Defining dimension
dimen = len(X)
max_iter = param.max_iter
R = param.restart
tol = param.tol
# Set number of outer and inner iterations
max_outer = max_iter
if R > dimen:
warn('Setting number of inner iterations (restrt) to maximum\
allowed, which is A.shape[0] ')
R = dimen
max_inner = R
# Prep for method
aux = gmres_dot(X, surf_array, field_array, ind0, param, timing, kernel)
r = b - aux
normr = norm(r)
# Check initial guess ( scaling by b, if b != 0, must account for
# case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol*normb:
return X
iteration = 0
#Here start the GMRES
for outer in range(max_outer):
# Preallocate for Givens Rotations, Hessenberg matrix and Krylov Space
# Space required is O(dimen*max_inner).
# NOTE: We are dealing with row-major matrices, so we traverse in a
# row-major fashion,
# i.e., H and V's transpose is what we store.
Q = [] # Initialzing Givens Rotations
# Upper Hessenberg matrix, which is then
# converted to upper triagonal with Givens Rotations
H = numpy.zeros((max_inner+1, max_inner+1), dtype=xtype)
V = numpy.zeros((max_inner+1, dimen), dtype=xtype) #Krylov space
# vs store the pointers to each column of V.
# This saves a considerable amount of time.
vs = []
# v = r/normr
V[0, :] = scal(1.0/normr, r) # scal wrapper of dscal --> x = a*x
vs.append(V[0, :])
#Saving initial residual to be used to calculate the rel_resid
if iteration==0:
res_0 = normb
#RHS vector in the Krylov space
g = numpy.zeros((dimen, ), dtype=xtype)
g[0] = normr
for inner in range(max_inner):
#New search direction
v= V[inner+1, :]
v[:] = gmres_dot(vs[-1], surf_array, field_array, ind0, param,
timing, kernel)
vs.append(v)
normv_old = norm(v)
#Modified Gram Schmidt
for k in range(inner+1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = alpha
v[:] = axpy(vk, v, dimen, -alpha) # y := a*x + y
#axpy is a wrapper for daxpy (blas function)
normv = norm(v)
H[inner, inner+1] = normv
#Check for breakdown
if H[inner, inner+1] != 0.0:
v[:] = scal(1.0/H[inner, inner+1], v)
#Apply for Givens rotations to H
if inner > 0:
apply_givens(Q, H[inner, :], inner)
#Calculate and apply next complex-valued Givens rotations
#If max_inner = dimen, we don't need to calculate, this
#is unnecessary for the last inner iteration when inner = dimen -1
if inner != dimen - 1:
if H[inner, inner+1] != 0:
#rotg is a blas function that computes the parameters
#for a Givens rotation
[c, s] = rotg(H[inner, inner], H[inner, inner+1])
Qblock = numpy.array([[c, s], [-numpy.conjugate(s),c]], dtype=xtype)
Q.append(Qblock)
#Apply Givens Rotations to RHS for the linear system in
# the krylov space.
g[inner:inner+2] = scipy.dot(Qblock, g[inner:inner+2])
#Apply Givens rotations to H
H[inner, inner] = dotu(Qblock[0,:], H[inner, inner:inner+2])
H[inner, inner+1] = 0.0
iteration+= 1
if inner < max_inner-1:
normr = abs(g[inner+1])
rel_resid = normr/res_0
if rel_resid < tol:
break
if iteration%1==0:
print ('Iteration: %i, relative residual: %s'%(iteration,rel_resid))
if (inner + 1 == R):
print('Residual: %f. Restart...' % rel_resid)
# end inner loop, back to outer loop
# Find best update to X in Krylov Space V. Solve inner X inner system.
y = scipy.linalg.solve (H[0:inner+1, 0:inner+1].T, g[0:inner+1])
update = numpy.ravel(scipy.mat(V[:inner+1, :]).T * y.reshape(-1,1))
X= X + update
aux = gmres_dot(X, surf_array, field_array, ind0, param, timing, kernel)
r = b - aux
normr = norm(r)
rel_resid = normr/res_0
# test for convergence
if rel_resid < tol:
print 'GMRES solve'
print('Converged after %i iterations to a residual of %s'%(iteration,rel_resid))
print 'Time weight vector: %f'%timing.time_mass
print 'Time sort : %f'%timing.time_sort
print 'Time data transfer: %f'%timing.time_trans
print 'Time P2M : %f'%timing.time_P2M
print 'Time M2M : %f'%timing.time_M2M
print 'Time M2P : %f'%timing.time_M2P
print 'Time P2P : %f'%timing.time_P2P
print '\tTime analy: %f'%timing.time_an
return X
#end outer loop
return X
def solve(self,
b,
x0=None,
tol=1e-5,
maxiter=100,
cycle='V',
accel=None,
callback=None,
residuals=None,
return_residuals=False):
"""Execute multigrid cycling.
Parameters
----------
b : array
Right hand side.
x0 : array
Initial guess.
tol : float
Stopping criteria: relative residual r[k]/r[0] tolerance.
maxiter : int
Stopping criteria: maximum number of allowable iterations.
cycle : {'V','W','F','AMLI'}
Type of multigrid cycle to perform in each iteration.
accel : string, function
Defines acceleration method. Can be a string such as 'cg'
or 'gmres' which is the name of an iterative solver in
pyamg.krylov (preferred) or scipy.sparse.linalg.isolve.
If accel is not a string, it will be treated like a function
with the same interface provided by the iterative solvers in SciPy.
callback : function
User-defined function called after each iteration. It is
called as callback(xk) where xk is the k-th iterate vector.
residuals : list
List to contain residual norms at each iteration.
Returns
-------
x : array
Approximate solution to Ax=b
See Also
--------
aspreconditioner
Examples
--------
>>> from numpy import ones
>>> from pyamg import ruge_stuben_solver
>>> from pyamg.gallery import poisson
>>> A = poisson((100, 100), format='csr')
>>> b = A * ones(A.shape[0])
>>> ml = ruge_stuben_solver(A, max_coarse=10)
>>> residuals = []
>>> x = ml.solve(b, tol=1e-12, residuals=residuals) # standalone solver
"""
from pyamg.util.linalg import residual_norm, norm
if x0 is None:
x = np.zeros_like(b)
else:
x = np.array(x0) # copy
cycle = str(cycle).upper()
# AMLI cycles require hermitian matrix
if (cycle == 'AMLI') and hasattr(self.levels[0].A, 'symmetry'):
if self.levels[0].A.symmetry != 'hermitian':
raise ValueError('AMLI cycles require \
symmetry to be hermitian')
if accel is not None:
# Check for symmetric smoothing scheme when using CG
if (accel == 'cg') and (not self.symmetric_smoothing):
warn('Incompatible non-symmetric multigrid preconditioner '
'detected, due to presmoother/postsmoother combination. '
'CG requires SPD preconditioner, not just SPD matrix.')
# Check for AMLI compatability
if (accel != 'fgmres') and (cycle == 'AMLI'):
raise ValueError('AMLI cycles require acceleration (accel) '
'to be fgmres, or no acceleration')
# py23 compatibility:
try:
basestring
except NameError:
basestring = str
# Acceleration is being used
kwargs = {}
if isinstance(accel, basestring):
from pyamg import krylov
from scipy.sparse.linalg import isolve
kwargs = {}
if hasattr(krylov, accel):
accel = getattr(krylov, accel)
else:
accel = getattr(isolve, accel)
kwargs['atol'] = 'legacy'
A = self.levels[0].A
M = self.aspreconditioner(cycle=cycle)
try: # try PyAMG style interface which has a residuals parameter
return accel(A,
b,
x0=x0,
tol=tol,
maxiter=maxiter,
M=M,
callback=callback,
residuals=residuals,
**kwargs)[0]
except BaseException:
# try the scipy.sparse.linalg.isolve style interface,
# which requires a call back function if a residual
# history is desired
cb = callback
if residuals is not None:
residuals[:] = [residual_norm(A, x, b)]
def callback(x):
if np.isscalar(x):
residuals.append(x)
else:
residuals.append(residual_norm(A, x, b))
if cb is not None:
cb(x)
return accel(A,
b,
x0=x0,
tol=tol,
maxiter=maxiter,
M=M,
callback=callback,
**kwargs)[0]
else:
# Scale tol by normb
# Don't scale tol earlier. The accel routine should also scale tol
normb = norm(b)
if normb != 0:
tol = tol * normb
if return_residuals:
warn('return_residuals is deprecated. Use residuals instead')
residuals = []
if residuals is None:
residuals = []
else:
residuals[:] = []
# Create uniform types for A, x and b
# Clearly, this logic doesn't handle the case of real A and complex b
from scipy.sparse.sputils import upcast
from pyamg.util.utils import to_type
tp = upcast(b.dtype, x.dtype, self.levels[0].A.dtype)
[b, x] = to_type(tp, [b, x])
b = np.ravel(b)
x = np.ravel(x)
A = self.levels[0].A
residuals.append(residual_norm(A, x, b))
self.first_pass = True
while len(residuals) <= maxiter and residuals[-1] > tol:
if len(self.levels) == 1:
# hierarchy has only 1 level
x = self.coarse_solver(A, b)
else:
self.__solve(0, x, b, cycle)
residuals.append(residual_norm(A, x, b))
self.first_pass = False
if callback is not None:
callback(x)
if return_residuals:
return x, residuals
else:
return x
def solve(self, b, x0=None, tol=1e-5, maxiter=100, cycle='V', accel=None,
callback=None, residuals=None, return_residuals=False):
"""Execute multigrid cycling.
Parameters
----------
b : array
Right hand side.
x0 : array
Initial guess.
tol : float
Stopping criteria: relative residual r[k]/r[0] tolerance.
maxiter : int
Stopping criteria: maximum number of allowable iterations.
cycle : {'V','W','F','AMLI'}
Type of multigrid cycle to perform in each iteration.
accel : string, function
Defines acceleration method. Can be a string such as 'cg'
or 'gmres' which is the name of an iterative solver in
pyamg.krylov (preferred) or scipy.sparse.linalg.isolve.
If accel is not a string, it will be treated like a function
with the same interface provided by the iterative solvers in SciPy.
callback : function
User-defined function called after each iteration. It is
called as callback(xk) where xk is the k-th iterate vector.
residuals : list
List to contain residual norms at each iteration.
Returns
-------
x : array
Approximate solution to Ax=b
See Also
--------
aspreconditioner
Examples
--------
>>> from numpy import ones
>>> from pyamg import ruge_stuben_solver
>>> from pyamg.gallery import poisson
>>> A = poisson((100, 100), format='csr')
>>> b = A * ones(A.shape[0])
>>> ml = ruge_stuben_solver(A, max_coarse=10)
>>> residuals = []
>>> x = ml.solve(b, tol=1e-12, residuals=residuals) # standalone solver
"""
from pyamg.util.linalg import residual_norm, norm
if x0 is None:
x = np.zeros_like(b)
else:
x = np.array(x0) # copy
cycle = str(cycle).upper()
# AMLI cycles require hermitian matrix
if (cycle == 'AMLI') and hasattr(self.levels[0].A, 'symmetry'):
if self.levels[0].A.symmetry != 'hermitian':
raise ValueError('AMLI cycles require \
symmetry to be hermitian')
if accel is not None:
# Check for symmetric smoothing scheme when using CG
if (accel is 'cg') and (not self.symmetric_smoothing):
warn('Incompatible non-symmetric multigrid preconditioner '
'detected, due to presmoother/postsmoother combination. '
'CG requires SPD preconditioner, not just SPD matrix.')
# Check for AMLI compatability
if (accel != 'fgmres') and (cycle == 'AMLI'):
raise ValueError('AMLI cycles require acceleration (accel) '
'to be fgmres, or no acceleration')
# py23 compatibility:
try:
basestring
except NameError:
basestring = str
# Acceleration is being used
kwargs = {}
if isinstance(accel, basestring):
from pyamg import krylov
from scipy.sparse.linalg import isolve
kwargs = {}
if hasattr(krylov, accel):
accel = getattr(krylov, accel)
else:
accel = getattr(isolve, accel)
kwargs['atol'] = 'legacy'
A = self.levels[0].A
M = self.aspreconditioner(cycle=cycle)
try: # try PyAMG style interface which has a residuals parameter
return accel(A, b, x0=x0, tol=tol, maxiter=maxiter, M=M,
callback=callback, residuals=residuals, **kwargs)[0]
except BaseException:
# try the scipy.sparse.linalg.isolve style interface,
# which requires a call back function if a residual
# history is desired
cb = callback
if residuals is not None:
residuals[:] = [residual_norm(A, x, b)]
def callback(x):
if sp.isscalar(x):
residuals.append(x)
else:
residuals.append(residual_norm(A, x, b))
if cb is not None:
cb(x)
return accel(A, b, x0=x0, tol=tol, maxiter=maxiter, M=M,
callback=callback, **kwargs)[0]
else:
# Scale tol by normb
# Don't scale tol earlier. The accel routine should also scale tol
normb = norm(b)
if normb != 0:
tol = tol * normb
if return_residuals:
warn('return_residuals is deprecated. Use residuals instead')
residuals = []
if residuals is None:
residuals = []
else:
residuals[:] = []
# Create uniform types for A, x and b
# Clearly, this logic doesn't handle the case of real A and complex b
from scipy.sparse.sputils import upcast
from pyamg.util.utils import to_type
tp = upcast(b.dtype, x.dtype, self.levels[0].A.dtype)
[b, x] = to_type(tp, [b, x])
b = np.ravel(b)
x = np.ravel(x)
A = self.levels[0].A
residuals.append(residual_norm(A, x, b))
self.first_pass = True
while len(residuals) <= maxiter and residuals[-1] > tol:
if len(self.levels) == 1:
# hierarchy has only 1 level
x = self.coarse_solver(A, b)
else:
self.__solve(0, x, b, cycle)
residuals.append(residual_norm(A, x, b))
self.first_pass = False
if callback is not None:
callback(x)
if return_residuals:
return x, residuals
else:
return x
def test_upcast(self):
assert_equal(sputils.upcast('intc'), np.intc)
assert_equal(sputils.upcast('int32', 'float32'), np.float64)
assert_equal(sputils.upcast('bool', complex, float), np.complex128)
assert_equal(sputils.upcast('i', 'd'), np.float64)
def _mul_vector(self, other):
# matrix * vector
result = np.zeros(self.shape[0], dtype=upcast(self.dtype, other.dtype))
for (i, j), v in iteritems(self):
result[i] += v * other[j]
return result
def gmres_mgs(A,
b,
x0=None,
tol=1e-5,
restrt=None,
maxiter=None,
xtype=None,
M=None,
callback=None,
residuals=None,
reorth=False):
'''
Generalized Minimum Residual Method (GMRES)
GMRES iteratively refines the initial solution guess to the system
Ax = b
Modified Gram-Schmidt version
Parameters
----------
A : {array, matrix, sparse matrix, LinearOperator}
n x n, linear system to solve
b : {array, matrix}
right hand side, shape is (n,) or (n,1)
x0 : {array, matrix}
initial guess, default is a vector of zeros
tol : float
relative convergence tolerance, i.e. tol is scaled by the norm
of the initial preconditioned residual
restrt : {None, int}
- if int, restrt is max number of inner iterations
and maxiter is the max number of outer iterations
- if None, do not restart GMRES, and max number of inner iterations
is maxiter
maxiter : {None, int}
- if restrt is None, maxiter is the max number of inner iterations
and GMRES does not restart
- if restrt is int, maxiter is the max number of outer iterations,
and restrt is the max number of inner iterations
xtype : type
dtype for the solution, default is automatic type detection
M : {array, matrix, sparse matrix, LinearOperator}
n x n, inverted preconditioner, i.e. solve M A x = M b.
callback : function
User-supplied function is called after each iteration as
callback(xk), where xk is the current solution vector
residuals : list
residuals contains the preconditioned residual norm history,
including the initial residual.
reorth : boolean
If True, then a check is made whether to re-orthogonalize the Krylov
space each GMRES iteration
Returns
-------
(xNew, info)
xNew : an updated guess to the solution of Ax = b
info : halting status of gmres
== =============================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead. This value
is precisely the order of the Krylov space.
<0 numerical breakdown, or illegal input
== =============================================
Notes
-----
- The LinearOperator class is in scipy.sparse.linalg.interface.
Use this class if you prefer to define A or M as a mat-vec routine
as opposed to explicitly constructing the matrix. A.psolve(..) is
still supported as a legacy.
- For robustness, modified Gram-Schmidt is used to orthogonalize the
Krylov Space Givens Rotations are used to provide the residual norm
each iteration
Examples
--------
>>> from pyamg.krylov import gmres
>>> from pyamg.util.linalg import norm
>>> import numpy as np
>>> from pyamg.gallery import poisson
>>> A = poisson((10,10))
>>> b = np.ones((A.shape[0],))
>>> (x,flag) = gmres(A,b, maxiter=2, tol=1e-8, orthog='mgs')
>>> print norm(b - A*x)
>>> 6.5428213057
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 151-172, pp. 272-275, 2003
http://www-users.cs.umn.edu/~saad/books.html
.. [2] C. T. Kelley, http://www4.ncsu.edu/~ctk/matlab_roots.html
'''
# Convert inputs to linear system, with error checking
A, M, x, b, postprocess = make_system(A, M, x0, b, xtype)
dimen = A.shape[0]
# Ensure that warnings are always reissued from this function
import warnings
warnings.filterwarnings('always', module='pyamg\.krylov\._gmres_mgs')
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
if not hasattr(M, 'dtype'):
Mtype = upcast(x.dtype, b.dtype)
else:
Mtype = M.dtype
xtype = upcast(Atype, x.dtype, b.dtype, Mtype)
if restrt is not None:
restrt = int(restrt)
if maxiter is not None:
maxiter = int(maxiter)
# Get fast access to underlying BLAS routines
# dotc is the conjugate dot, dotu does no conjugation
[lartg] = get_lapack_funcs(['lartg'], [x])
if np.iscomplexobj(np.zeros((1, ), dtype=xtype)):
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dotu', 'dotc', 'scal'], [x])
else:
# real type
[axpy, dotu, dotc, scal] =\
get_blas_funcs(['axpy', 'dot', 'dot', 'scal'], [x])
# Make full use of direct access to BLAS by defining own norm
def norm(z):
return np.sqrt(np.real(dotc(z, z)))
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# Set number of outer and inner iterations
if restrt:
if maxiter:
max_outer = maxiter
else:
max_outer = 1
if restrt > dimen:
warn('Setting number of inner iterations (restrt) to maximum\
allowed, which is A.shape[0] ')
restrt = dimen
max_inner = restrt
else:
max_outer = 1
if maxiter > dimen:
warn('Setting number of inner iterations (maxiter) to maximum\
allowed, which is A.shape[0] ')
maxiter = dimen
elif maxiter is None:
maxiter = min(dimen, 40)
max_inner = maxiter
# Is this a one dimensional matrix?
if dimen == 1:
entry = np.ravel(A * np.array([1.0], dtype=xtype))
return (postprocess(b / entry), 0)
# Prep for method
r = b - np.ravel(A * x)
# Apply preconditioner
r = np.ravel(M * r)
normr = norm(r)
if keep_r:
residuals.append(normr)
# Check for nan, inf
# if isnan(r).any() or isinf(r).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol * normb:
return (postprocess(x), 0)
# Scale tol by ||r_0||_2, we use the preconditioned residual
# because this is left preconditioned GMRES.
if normr != 0.0:
tol = tol * normr
# Use separate variable to track iterations. If convergence fails, we
# cannot simply report niter = (outer-1)*max_outer + inner. Numerical
# error could cause the inner loop to halt while the actual ||r|| > tol.
niter = 0
# Begin GMRES
for outer in range(max_outer):
# Preallocate for Givens Rotations, Hessenberg matrix and Krylov Space
# Space required is O(dimen*max_inner).
# NOTE: We are dealing with row-major matrices, so we traverse in a
# row-major fashion,
# i.e., H and V's transpose is what we store.
Q = [] # Givens Rotations
# Upper Hessenberg matrix, which is then
# converted to upper tri with Givens Rots
H = np.zeros((max_inner + 1, max_inner + 1), dtype=xtype)
V = np.zeros((max_inner + 1, dimen), dtype=xtype) # Krylov Space
# vs store the pointers to each column of V.
# This saves a considerable amount of time.
vs = []
# v = r/normr
V[0, :] = scal(1.0 / normr, r)
vs.append(V[0, :])
# This is the RHS vector for the problem in the Krylov Space
g = np.zeros((dimen, ), dtype=xtype)
g[0] = normr
for inner in range(max_inner):
# New Search Direction
v = V[inner + 1, :]
v[:] = np.ravel(M * (A * vs[-1]))
vs.append(v)
normv_old = norm(v)
# Check for nan, inf
# if isnan(V[inner+1, :]).any() or isinf(V[inner+1, :]).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Modified Gram Schmidt
for k in range(inner + 1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = alpha
v[:] = axpy(vk, v, dimen, -alpha)
normv = norm(v)
H[inner, inner + 1] = normv
# Re-orthogonalize
if (reorth is True) and (normv_old == normv_old + 0.001 * normv):
for k in range(inner + 1):
vk = vs[k]
alpha = dotc(vk, v)
H[inner, k] = H[inner, k] + alpha
v[:] = axpy(vk, v, dimen, -alpha)
# Check for breakdown
if H[inner, inner + 1] != 0.0:
v[:] = scal(1.0 / H[inner, inner + 1], v)
# Apply previous Givens rotations to H
if inner > 0:
apply_givens(Q, H[inner, :], inner)
# Calculate and apply next complex-valued Givens Rotation
# ==> Note that if max_inner = dimen, then this is unnecessary
# for the last inner
# iteration, when inner = dimen-1.
if inner != dimen - 1:
if H[inner, inner + 1] != 0:
[c, s, r] = lartg(H[inner, inner], H[inner, inner + 1])
Qblock = np.array([[c, s], [-np.conjugate(s), c]],
dtype=xtype)
Q.append(Qblock)
# Apply Givens Rotation to g,
# the RHS for the linear system in the Krylov Subspace.
g[inner:inner + 2] = np.dot(Qblock, g[inner:inner + 2])
# Apply effect of Givens Rotation to H
H[inner, inner] = dotu(Qblock[0, :], H[inner,
inner:inner + 2])
H[inner, inner + 1] = 0.0
niter += 1
# Don't update normr if last inner iteration, because
# normr is calculated directly after this loop ends.
if inner < max_inner - 1:
normr = np.abs(g[inner + 1])
if normr < tol:
break
# Allow user access to the iterates
if callback is not None:
callback(x)
if keep_r:
residuals.append(normr)
# end inner loop, back to outer loop
# Find best update to x in Krylov Space V. Solve inner x inner system.
y = sp.linalg.solve(H[0:inner + 1, 0:inner + 1].T, g[0:inner + 1])
update = np.ravel(np.mat(V[:inner + 1, :]).T * y.reshape(-1, 1))
x = x + update
r = b - np.ravel(A * x)
# Apply preconditioner
r = np.ravel(M * r)
normr = norm(r)
# Check for nan, inf
# if isnan(r).any() or isinf(r).any():
# warn('inf or nan after application of preconditioner')
# return(postprocess(x), -1)
# Allow user access to the iterates
if callback is not None:
callback(x)
if keep_r:
residuals.append(normr)
# Has GMRES stagnated?
indices = (x != 0)
if indices.any():
change = np.max(np.abs(update[indices] / x[indices]))
if change < 1e-12:
# No change, halt
return (postprocess(x), -1)
# test for convergence
if normr < tol:
return (postprocess(x), 0)
# end outer loop
return (postprocess(x), niter)
def solve(self,
b,
x0=None,
tol=1e-5,
maxiter=100,
cycle='V',
accel=None,
callback=None,
residuals=None,
return_info=False):
"""Execute multigrid cycling.
Parameters
----------
b : array
Right hand side.
x0 : array
Initial guess.
tol : float
Stopping criteria: relative residual r[k]/||b|| tolerance.
If `accel` is used, the stopping criteria is set by the Krylov method.
maxiter : int
Stopping criteria: maximum number of allowable iterations.
cycle : {'V','W','F','AMLI'}
Type of multigrid cycle to perform in each iteration.
accel : string, function
Defines acceleration method. Can be a string such as 'cg'
or 'gmres' which is the name of an iterative solver in
pyamg.krylov (preferred) or scipy.sparse.linalg._isolve.
If accel is not a string, it will be treated like a function
with the same interface provided by the iterative solvers in SciPy.
callback : function
User-defined function called after each iteration. It is
called as callback(xk) where xk is the k-th iterate vector.
residuals : list
List to contain residual norms at each iteration. The residuals
will be the residuals from the Krylov iteration -- see the `accel`
method to see verify whether this ||r|| or ||Mr|| (as in the case of
GMRES).
return_info : bool
If true, will return (x, info)
If false, will return x (default)
Returns
-------
x : array
Approximate solution to Ax=b after k iterations
info : string
Halting status
== =======================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead.
== =======================================
See Also
--------
aspreconditioner
Examples
--------
>>> from numpy import ones
>>> from pyamg import ruge_stuben_solver
>>> from pyamg.gallery import poisson
>>> A = poisson((100, 100), format='csr')
>>> b = A * ones(A.shape[0])
>>> ml = ruge_stuben_solver(A, max_coarse=10)
>>> residuals = []
>>> x = ml.solve(b, tol=1e-12, residuals=residuals) # standalone solver
"""
if x0 is None:
x = np.zeros_like(b)
else:
x = np.array(x0) # copy
A = self.levels[0].A
cycle = str(cycle).upper()
# AMLI cycles require hermitian matrix
if (cycle == 'AMLI') and hasattr(A, 'symmetry'):
if A.symmetry != 'hermitian':
raise ValueError('AMLI cycles require \
symmetry to be hermitian')
if accel is not None:
# Check for symmetric smoothing scheme when using CG
if (accel == 'cg') and (not self.symmetric_smoothing):
warn('Incompatible non-symmetric multigrid preconditioner '
'detected, due to presmoother/postsmoother combination. '
'CG requires SPD preconditioner, not just SPD matrix.')
# Check for AMLI compatability
if (accel != 'fgmres') and (cycle == 'AMLI'):
raise ValueError('AMLI cycles require acceleration (accel) '
'to be fgmres, or no acceleration')
# Acceleration is being used
kwargs = {}
if isinstance(accel, str):
kwargs = {}
if hasattr(krylov, accel):
accel = getattr(krylov, accel)
else:
accel = getattr(_isolve, accel)
kwargs['atol'] = 'legacy'
M = self.aspreconditioner(cycle=cycle)
try: # try PyAMG style interface which has a residuals parameter
x, info = accel(A,
b,
x0=x0,
tol=tol,
maxiter=maxiter,
M=M,
callback=callback,
residuals=residuals,
**kwargs)
if return_info:
return x, info
return x
except TypeError:
# try the scipy.sparse.linalg._isolve style interface,
# which requires a callback function if a residual
# history is desired
if residuals is not None:
residuals[:] = [np.linalg.norm(b - A @ x)]
def callback_wrapper(x):
if np.isscalar(x):
residuals.append(x)
else:
residuals.append(np.linalg.norm(b - A @ x))
if callback is not None:
callback(x)
else:
callback_wrapper = callback
x, info = accel(A,
b,
x0=x0,
tol=tol,
maxiter=maxiter,
M=M,
callback=callback_wrapper,
**kwargs)
if return_info:
return x, info
return x
else:
# Scale tol by normb
# Don't scale tol earlier. The accel routine should also scale tol
normb = np.linalg.norm(b)
if normb == 0.0:
normb = 1.0 # set so that we have an absolute tolerance
# Start cycling (no acceleration)
normr = np.linalg.norm(b - A @ x)
if residuals is not None:
residuals[:] = [normr] # initial residual
# Create uniform types for A, x and b
# Clearly, this logic doesn't handle the case of real A and complex b
tp = upcast(b.dtype, x.dtype, A.dtype)
[b, x] = to_type(tp, [b, x])
b = np.ravel(b)
x = np.ravel(x)
it = 0
while True: # it <= maxiter and normr >= tol:
if len(self.levels) == 1:
# hierarchy has only 1 level
x = self.coarse_solver(A, b)
else:
self.__solve(0, x, b, cycle)
it += 1
normr = np.linalg.norm(b - A @ x)
if residuals is not None:
residuals.append(normr)
if callback is not None:
callback(x)
if normr < tol * normb:
if return_info:
return x, 0
return x
if it == maxiter:
if return_info:
return x, it
return x
def mybmat(blocks, format=None, dtype=None):
# bugfix-Zeile
if len(blocks) > 0:
numcols = [None for _ in blocks[0]]
for row in blocks:
for colnr, col in enumerate(row):
if col is not None:
numcols[colnr] = col.shape[1]
assert not (None in numcols)
blocks.append([np.zeros(shape=(0, i)) for i in numcols])
blocks = np.asarray(blocks, dtype='object')
if np.ndim(blocks) != 2:
raise ValueError('blocks must have rank 2')
M, N = blocks.shape
block_mask = np.zeros(blocks.shape, dtype=np.bool)
brow_lengths = np.zeros(blocks.shape[0], dtype=np.intc)
bcol_lengths = np.zeros(blocks.shape[1], dtype=np.intc)
# convert everything to COO format
for i in range(M):
for j in range(N):
if blocks[i, j] is not None:
A = coo_matrix(blocks[i, j])
blocks[i, j] = A
block_mask[i, j] = True
if brow_lengths[i] == 0:
brow_lengths[i] = A.shape[0]
else:
if brow_lengths[i] != A.shape[0]:
raise ValueError('blocks[%d,:] has incompatible row dimensions' % i)
if bcol_lengths[j] == 0:
bcol_lengths[j] = A.shape[1]
else:
if bcol_lengths[j] != A.shape[1]:
raise ValueError('blocks[:,%d] has incompatible column dimensions' % j)
nnz = sum([A.nnz for A in blocks[block_mask]])
if dtype is None:
dtype = upcast(*tuple([A.dtype for A in blocks[block_mask]]))
row_offsets = np.concatenate(([0], np.cumsum(brow_lengths)))
col_offsets = np.concatenate(([0], np.cumsum(bcol_lengths)))
data = np.empty(nnz, dtype=dtype)
row = np.empty(nnz, dtype=np.intc)
col = np.empty(nnz, dtype=np.intc)
nnz = 0
for i in range(M):
for j in range(N):
if blocks[i, j] is not None:
A = blocks[i, j]
data[nnz:nnz + A.nnz] = A.data
row[nnz:nnz + A.nnz] = A.row
col[nnz:nnz + A.nnz] = A.col
row[nnz:nnz + A.nnz] += row_offsets[i]
col[nnz:nnz + A.nnz] += col_offsets[j]
nnz += A.nnz
shape = (np.sum(brow_lengths), np.sum(bcol_lengths))
return coo_matrix((data, (row, col)), shape=shape).asformat(format)
def cgnr(A, b, x0=None, tol=1e-5, maxiter=None, xtype=None, M=None,
callback=None, residuals=None):
'''Conjugate Gradient, Normal Residual algorithm
Applies CG to the normal equations, A.H A x = b. Left preconditioning
is supported. Note that unless A is well-conditioned, the use of
CGNR is inadvisable
Parameters
----------
A : {array, matrix, sparse matrix, LinearOperator}
n x n, linear system to solve
b : {array, matrix}
right hand side, shape is (n,) or (n,1)
x0 : {array, matrix}
initial guess, default is a vector of zeros
tol : float
relative convergence tolerance, i.e. tol is scaled by ||r_0||_2
maxiter : int
maximum number of allowed iterations
xtype : type
dtype for the solution, default is automatic type detection
M : {array, matrix, sparse matrix, LinearOperator}
n x n, inverted preconditioner, i.e. solve M A.H A x = b.
callback : function
User-supplied function is called after each iteration as
callback(xk), where xk is the current solution vector
residuals : list
residuals has the residual norm history,
including the initial residual, appended to it
Returns
-------
(xNew, info)
xNew : an updated guess to the solution of Ax = b
info : halting status of cgnr
== =======================================
0 successful exit
>0 convergence to tolerance not achieved,
return iteration count instead.
<0 numerical breakdown, or illegal input
== =======================================
Notes
-----
The LinearOperator class is in scipy.sparse.linalg.interface.
Use this class if you prefer to define A or M as a mat-vec routine
as opposed to explicitly constructing the matrix. A.psolve(..) is
still supported as a legacy.
Examples
--------
>>> from pyamg.krylov.cgnr import cgnr
>>> from pyamg.util.linalg import norm
>>> import numpy as np
>>> from pyamg.gallery import poisson
>>> A = poisson((10,10))
>>> b = np.ones((A.shape[0],))
>>> (x,flag) = cgnr(A,b, maxiter=2, tol=1e-8)
>>> print norm(b - A*x)
9.3910201849
References
----------
.. [1] Yousef Saad, "Iterative Methods for Sparse Linear Systems,
Second Edition", SIAM, pp. 276-7, 2003
http://www-users.cs.umn.edu/~saad/books.html
'''
# Store the conjugate transpose explicitly as it will be used much later on
if isspmatrix(A):
AH = A.H
else:
# TODO avoid doing this since A may be a different sparse type
AH = aslinearoperator(asmatrix(A).H)
# Convert inputs to linear system, with error checking
A, M, x, b, postprocess = make_system(A, M, x0, b)
dimen = A.shape[0]
# Ensure that warnings are always reissued from this function
import warnings
warnings.filterwarnings('always', module='pyamg\.krylov\._cgnr')
# Choose type
if not hasattr(A, 'dtype'):
Atype = upcast(x.dtype, b.dtype)
else:
Atype = A.dtype
if not hasattr(M, 'dtype'):
Mtype = upcast(x.dtype, b.dtype)
else:
Mtype = M.dtype
xtype = upcast(Atype, x.dtype, b.dtype, Mtype)
# Should norm(r) be kept
if residuals == []:
keep_r = True
else:
keep_r = False
# How often should r be recomputed
recompute_r = 8
# Check iteration numbers. CGNR suffers from loss of orthogonality quite
# easily, so we arbitrarily let the method go up to 130% over the
# theoretically necessary limit of maxiter=dimen
if maxiter is None:
maxiter = int(ceil(1.3*dimen)) + 2
elif maxiter < 1:
raise ValueError('Number of iterations must be positive')
elif maxiter > (1.3*dimen):
warn('maximum allowed inner iterations (maxiter) are the 130% times \
the number of dofs')
maxiter = int(ceil(1.3*dimen)) + 2
# Prep for method
r = b - A*x
rhat = AH*r
normr = norm(r)
if keep_r:
residuals.append(normr)
# Check initial guess ( scaling by b, if b != 0,
# must account for case when norm(b) is very small)
normb = norm(b)
if normb == 0.0:
normb = 1.0
if normr < tol*normb:
if callback is not None:
callback(x)
return (postprocess(x), 0)
# Scale tol by ||r_0||_2
if normr != 0.0:
tol = tol*normr
# Begin CGNR
# Apply preconditioner and calculate initial search direction
z = M*rhat
p = z.copy()
old_zr = inner(z.conjugate(), rhat)
for iter in range(maxiter):
# w_j = A p_j
w = A*p
# alpha = (z_j, rhat_j) / (w_j, w_j)
alpha = old_zr / inner(w.conjugate(), w)
# x_{j+1} = x_j + alpha*p_j
x += alpha*p
# r_{j+1} = r_j - alpha*w_j
if mod(iter, recompute_r) and iter > 0:
r -= alpha*w
else:
r = b - A*x
# rhat_{j+1} = A.H*r_{j+1}
rhat = AH*r
# z_{j+1} = M*r_{j+1}
z = M*rhat
# beta = (z_{j+1}, rhat_{j+1}) / (z_j, rhat_j)
new_zr = inner(z.conjugate(), rhat)
beta = new_zr / old_zr
old_zr = new_zr
# p_{j+1} = A.H*z_{j+1} + beta*p_j
p *= beta
p += z
# Allow user access to residual
if callback is not None:
callback(x)
# test for convergence
normr = norm(r)
if keep_r:
residuals.append(normr)
if normr < tol:
return (postprocess(x), 0)
# end loop
return (postprocess(x), iter+1)