def subdivision_solve_1d(f,a,b,deg,interval_data,root_tracker,tols,max_level,level=0):
"""Finds the roots of a one-dimensional function using subdivision and chebyshev approximation.
Parameters
----------
f : function from R -> R
The function to interpolate.
a : numpy array
The lower bound on the interval.
b : numpy array
The upper bound on the interval.
deg : int
The degree of the approximation.
interval_data : IntervalData
A class to run the subinterval checks and keep track of the solve progress
root_tracker : RootTracker
A class to keep track of the roots that are found.
tols : Tolerances
The tolerances to be used.
max_level : int
The maximum level for the recursion
level : int
The current level of the recursion.
Returns
-------
coeffs : numpy array
The coefficient of the chebyshev interpolating polynomial.
"""
if level > max_level:
# TODO Refine case where there may be a root and it goes too deep.
interval_data.track_interval("Too Deep", [a, b])
return
RAND = 0.5139303900908738
interval_data.print_progress()
coeff, inf_norm = interval_approximate_1d(f,a,b,deg)
coeff2, inf_norm = interval_approximate_1d(f,a,b,deg*2,inf_norm)
coeff2[slice_top(coeff)] -= coeff
error = np.sum(np.abs(coeff2))
if error > tols.abs_approx_tol+tols.rel_approx_tol*inf_norm:
#Subdivide the interval and recursively call the function.
div_spot = a + (b-a)*RAND
subdivision_solve_1d(f,a,div_spot,deg,interval_data,root_tracker,tols,max_level,level+1)
subdivision_solve_1d(f,div_spot,b,deg,interval_data,root_tracker,tols,max_level,level+1)
else:
while error + abs(coeff[-1]) < tols.abs_approx_tol+tols.rel_approx_tol*inf_norm and len(coeff) > 5:
error += abs(coeff[-1])
coeff = coeff[:-1]
try:
good_zeros_tol = max(tols.min_good_zeros_tol, error*tols.good_zeros_factor)
zeros = transform(good_zeros_1d(multCheb(coeff),good_zeros_tol,good_zeros_tol),a,b)
interval_data.track_interval('Spectral', [a,b])
root_tracker.add_roots(zeros, a, b, 'Spectral')
except ConditioningError as e:
div_spot = a + (b-a)*RAND
subdivision_solve_1d(f,a,div_spot,deg,interval_data,root_tracker,tols,max_level,level+1)
subdivision_solve_1d(f,div_spot,b,deg,interval_data,root_tracker,tols,max_level,level+1)
def full_cheb_approximate(f,
a,
b,
deg,
abs_approx_tol,
rel_approx_tol,
good_deg=None):
"""Gives the full chebyshev approximation and checks if it's good enough.
Parameters
----------
f : function
The function we approximate.
a : numpy array
The lower bound on the interval.
b : numpy array
The upper bound on the interval.
deg : int
The degree to approximate with.
rel_approx_tol : float or list
The relative tolerance used in the approximation tolerance. The error is bouned by
error < abs_approx_tol + rel_approx_tol * inf_norm_of_approximation
abs_approx_tol : float or list
The absolute tolerance used in the approximation tolerance. The error is bouned by
error < abs_approx_tol + rel_approx_tol * inf_norm_of_approximation
good_deg : numpy array
Interpoation degree that is guaranteed to give an approximation valid
to within approx_tol.
Returns
-------
coeff : numpy array
The coefficient array of the interpolation. If it can't get a good
approximation and needs to subdivide, returns None.
inf_norm : float
The inf norm of f on [a, b]
error : float
The approximation error
"""
# We don't know what degree we want
if good_deg is None:
good_deg = deg
# Try degree deg and see if it's good enough
coeff = interval_approximate_nd(f, a, b, good_deg)
coeff2, inf_norm = interval_approximate_nd(f,
a,
b,
good_deg * 2,
return_inf_norm=True)
coeff2[slice_top(coeff.shape)] -= coeff
error = np.sum(np.abs(coeff2))
if error > abs_approx_tol + rel_approx_tol * inf_norm:
return None, inf_norm, error
else:
return coeff, inf_norm, error
def _mon_mult1(initial_matrix, idx, dim_mult):
"""
Executes monomial multiplication in one dimension.
Parameters
----------
initial_matrix : array_like
Matrix of coefficients that represent a Chebyshev polynomial.
idx : tuple of ints
The index of a monomial of one variable to multiply by initial_matrix.
dim_mult : int
The location of the non-zero value in idx.
Returns
-------
ndarray
Coeff that are the result of the one dimensial monomial multiplication.
"""
p1 = np.zeros(initial_matrix.shape + idx)
p1[slice_bottom(initial_matrix)] = initial_matrix
largest_idx = [i - 1 for i in initial_matrix.shape]
new_shape = [
max(i, j)
for i, j in itertools.zip_longest(largest_idx, idx, fillvalue=0)
] #finds the largest length in each dimmension
if initial_matrix.shape[dim_mult] <= idx[dim_mult]:
add_a = [
i - j for i, j in itertools.zip_longest(
new_shape, largest_idx, fillvalue=0)
]
add_a_list = np.zeros((len(new_shape), 2))
#changes the second column to the values of add_a and add_b.
add_a_list[:, 1] = add_a
#uses add_a_list and add_b_list to pad each polynomial appropriately.
initial_matrix = np.pad(initial_matrix, add_a_list.astype(int),
'constant')
number_of_dim = initial_matrix.ndim
shape_of_self = initial_matrix.shape
#Loop iterates through each dimension of the polynomial and folds in that dimension
for i in range(number_of_dim):
if idx[i] != 0:
initial_matrix = MultiCheb._fold_in_i_dir(
initial_matrix, number_of_dim, i, shape_of_self[i], idx[i])
if p1.shape != initial_matrix.shape:
idx = [i - j for i, j in zip(p1.shape, initial_matrix.shape)]
result = np.zeros(np.array(initial_matrix.shape) + idx)
result[slice_top(initial_matrix)] = initial_matrix
initial_matrix = result
Pf = p1 + initial_matrix
return .5 * Pf
def create_matrix(poly_coeffs, degree, dim, divisor_var):
''' Builds a Macaulay matrix for reduction.
Parameters
----------
poly_coeffs : list.
Contains numpy arrays that hold the coefficients of the polynomials to be put in the matrix.
degree : int
The degree of the Macaulay Matrix
dim : int
The dimension of the polynomials going into the matrix.
divisor_var : int
What variable is being divided by. 0 is x, 1 is y, etc. Defaults to x.
Returns
-------
matrix : 2D numpy array
The Macaulay matrix.
matrix_terms : numpy array
The ith row is the term represented by the ith column of the matrix.
cuts : tuple
When the matrix is reduced it is split into 3 parts with restricted pivoting. These numbers indicate
where those cuts happen.
'''
bigShape = [degree + 1] * dim
matrix_terms, cuts = get_matrix_terms(poly_coeffs, dim, divisor_var)
#Get the slices needed to pull the matrix_terms from the coeff matrix.
matrix_term_indexes = list()
for row in matrix_terms.T:
matrix_term_indexes.append(row)
#Adds the poly_coeffs to flat_polys, using added_zeros to make sure every term is in there.
added_zeros = np.zeros(bigShape)
flat_polys = list()
for coeff in poly_coeffs:
slices = slice_top(coeff)
added_zeros[slices] = coeff
flat_polys.append(added_zeros[tuple(matrix_term_indexes)])
added_zeros[slices] = np.zeros_like(coeff)
del poly_coeffs
#Make the matrix. Reshape is faster than stacking.
matrix = np.reshape(flat_polys, (len(flat_polys), len(matrix_terms)))
#Sorts the rows of the matrix so it is close to upper triangular.
matrix = row_swap_matrix(matrix)
return matrix, matrix_terms, cuts
def create_matrix(poly_coeffs, degree, dim, varsToRemove):
''' Builds a Macaulay matrix.
Parameters
----------
poly_coeffs : list.
Contains numpy arrays that hold the coefficients of the polynomials to be put in the matrix.
degree : int
The degree of the Macaulay Matrix
dim : int
The dimension of the polynomials going into the matrix.
varsToRemove : list
The variables to remove from the basis because we have linear polysnomials
Returns
-------
matrix : 2D numpy array
The Macaulay matrix.
matrix_terms : numpy array
The ith row is the term represented by the ith column of the matrix.
cut : int
Number of monomials of highest degree
'''
bigShape = [degree + 1] * dim
matrix_terms, cut = sorted_matrix_terms(degree, dim, varsToRemove)
#Get the slices needed to pull the matrix_terms from the coeff matrix.
matrix_term_indexes = list()
for row in matrix_terms.T:
matrix_term_indexes.append(row)
#Adds the poly_coeffs to flat_polys, using added_zeros to make sure every term is in there.
added_zeros = np.zeros(bigShape)
flat_polys = list()
for coeff in poly_coeffs:
slices = slice_top(coeff)
added_zeros[slices] = coeff
flat_polys.append(added_zeros[tuple(matrix_term_indexes)])
added_zeros[slices] = np.zeros_like(coeff)
del poly_coeffs
#Make the matrix. Reshape is faster than stacking.
matrix = np.reshape(flat_polys, (len(flat_polys), len(matrix_terms)))
#Sorts the rows of the matrix so it is close to upper triangular.
matrix = row_swap_matrix(matrix)
return matrix, matrix_terms, cut
def subdivision_solve_1d(f,
a,
b,
deg,
target_deg,
interval_data,
root_tracker,
tols,
max_level,
level=0,
method='svd',
trust_small_evals=False):
"""Finds the roots of a one-dimensional function using subdivision and
chebyshev approximation.
Parameters
----------
f : function from R -> R
The function to interpolate.
a : numpy array
The lower bound on the interval.
b : numpy array
The upper bound on the interval.
deg : int
The degree of the approximation.
target_deg : int
The degree to subdivide down to before building the Macauly matrix.
interval_data : IntervalData
A class to run the subinterval checks and keep track of the solve progress
root_tracker : RootTracker
A class to keep track of the roots that are found.
tols : Tolerances
The tolerances to be used.
max_level : int
The maximum level for the recursion
level : int
The current level of the recursion.
Returns
-------
coeffs : numpy array
The coefficient of the chebyshev interpolating polynomial.
"""
if level > max_level:
# TODO Refine case where there may be a root and it goes too deep.
interval_data.track_interval("Too Deep", [a, b])
return
# Determine the point at which to subdivide the interval
RAND = 0.5139303900908738
interval_data.print_progress()
# Approximate the function using Chebyshev polynomials
coeff = interval_approximate_1d(f, a, b, deg)
coeff2, sign_change, inf_norm = interval_approximate_1d(
f, a, b, deg * 2, return_bools=True, return_inf_norm=True)
coeff2[slice_top(coeff.shape)] -= coeff
# Calculate the approximate error between the deg and 2*deg approximations
error = np.sum(np.abs(coeff2))
allowed_error = tols.abs_approx_tol + tols.rel_approx_tol * inf_norm
if error > allowed_error:
# Subdivide the interval and recursively call the function.
div_spot = a + (b - a) * RAND
good_deg = deg
subdivision_solve_1d(f, a, div_spot, good_deg, target_deg,
interval_data, root_tracker, tols, max_level,
level + 1)
subdivision_solve_1d(f, div_spot, b, good_deg, target_deg,
interval_data, root_tracker, tols, max_level,
level + 1)
else:
# Trim the coefficient array (reduce the degree) as much as we can.
# This identifies a 'good degree' with which to approximate the function
# if it is less than the given approx degree.
last_coeff_size = abs(coeff[-1])
new_error = error + last_coeff_size
while new_error < allowed_error:
if len(coeff) == 1:
break
#maybe a list pop here? idk if worth it to switch away from arrays
coeff = coeff[:-1]
last_coeff_size = abs(coeff[-1])
error = new_error
new_error = error + last_coeff_size
if not trust_small_evals:
error = max(error, macheps)
good_deg = max(len(coeff) - 1, 1)
# Run interval checks to eliminate regions
if not sign_change: # Skip checks if there is a sign change
if interval_data.check_interval(coeff, error, a, b):
return
try:
good_zeros_tol = max(tols.min_good_zeros_tol,
error * tols.good_zeros_factor)
zeros = transform(
good_zeros_1d(multCheb(coeff), good_zeros_tol, good_zeros_tol),
a, b)
interval_data.track_interval("Macaulay", [a, b])
root_tracker.add_roots(zeros, a, b, "Macaulay")
except (ConditioningError, TooManyRoots) as e:
div_spot = a + (b - a) * RAND
subdivision_solve_1d(f, a, div_spot, good_deg, target_deg,
interval_data, root_tracker, tols, max_level,
level + 1)
subdivision_solve_1d(f, div_spot, b, good_deg, target_deg,
interval_data, root_tracker, tols, max_level,
level + 1)
def full_cheb_approximate(f,
a,
b,
deg,
abs_approx_tol,
rel_approx_tol,
good_deg=None):
"""Gives the full chebyshev approximation and checks if it's good enough.
Parameters
----------
f : function
The function we approximate.
a : numpy array
The lower bound on the interval.
b : numpy array
The upper bound on the interval.
deg : int
The degree to approximate with.
rel_approx_tol : float or list
The relative tolerance used in the approximation tolerance. The error is bouned by
error < abs_approx_tol + rel_approx_tol * inf_norm_of_approximation
abs_approx_tol : float or list
The absolute tolerance used in the approximation tolerance. The error is bouned by
error < abs_approx_tol + rel_approx_tol * inf_norm_of_approximation
good_deg : numpy array
Interpoation degree that is guaranteed to give an approximation valid to within approx_tol.
Returns
-------
coeff : numpy array
The coefficient array of the interpolation. If it can't get a good approximation and needs to subdivide, returns None.
bools: numpy array
(2^n, 1) array of bools corresponding to which subintervals the function changes sign in
If it cannot get a good approximation, it returns which directions to subdivide in.
inf_norm : float
The inf norm of f on [a,b]
error : float
The approximation error
"""
#We know what degree we want
# if good_deg is not None:
# coeff, bools, inf_norm = interval_approximate_nd(f,a,b,good_deg,return_bools=True)
# return coeff, bools, inf_norm
#Try degree deg and see if it's good enough
coeff, inf_norm = interval_approximate_nd(f, a, b, deg)
coeff2, bools, inf_norm = interval_approximate_nd(f,
a,
b,
deg * 2,
return_bools=True,
inf_norm=inf_norm)
# print(coeff)
# print(coeff2)
coeff2[slice_top(coeff)] -= coeff
error = np.sum(np.abs(coeff2))
if error > abs_approx_tol + rel_approx_tol * inf_norm:
#Find the directions to subdivide
dim = len(a)
# TODO: Intelligent Subdivision.
# div_dimensions = []
# slices = [slice(0,None,None)]*dim
# for d in range(dim):
# slices[d] = slice(deg+1,None,None)
# if np.sum(np.abs(coeff2[tuple(slices)])) > approx_tol/dim:
# div_dimensions.append(d)
# slices[d] = slice(0,None,None)
# if len(div_dimensions) == 0:
# div_dimensions.append(0)
# return None, np.array(div_dimensions)
#for now, subdivide in every dimension
return None, np.arange(dim), inf_norm, error
else:
return coeff, bools, inf_norm, error
