def __init__(self,
problem,
*,
solver_parameters=None,
options_prefix=None,
nullspace=None,
transpose_nullspace=None,
near_nullspace=None,
appctx=None,
pre_jacobian_callback=None,
post_jacobian_callback=None,
pre_function_callback=None,
post_function_callback=None):
r"""
:arg problem: A :class:`NonlinearVariationalProblem` to solve.
:kwarg nullspace: an optional :class:`.VectorSpaceBasis` (or
:class:`.MixedVectorSpaceBasis`) spanning the null
space of the operator.
:kwarg transpose_nullspace: as for the nullspace, but used to
make the right hand side consistent.
:kwarg near_nullspace: as for the nullspace, but used to
specify the near nullspace (for multigrid solvers).
:kwarg solver_parameters: Solver parameters to pass to PETSc.
This should be a dict mapping PETSc options to values.
:kwarg appctx: A dictionary containing application context that
is passed to the preconditioner if matrix-free.
:kwarg options_prefix: an optional prefix used to distinguish
PETSc options. If not provided a unique prefix will be
created. Use this option if you want to pass options
to the solver from the command line in addition to
through the ``solver_parameters`` dict.
:kwarg pre_jacobian_callback: A user-defined function that will
be called immediately before Jacobian assembly. This can
be used, for example, to update a coefficient function
that has a complicated dependence on the unknown solution.
:kwarg post_jacobian_callback: As above, but called after the
Jacobian has been assembled.
:kwarg pre_function_callback: As above, but called immediately
before residual assembly.
:kwarg post_function_callback: As above, but called immediately
after residual assembly.
Example usage of the ``solver_parameters`` option: to set the
nonlinear solver type to just use a linear solver, use
.. code-block:: python3
{'snes_type': 'ksponly'}
PETSc flag options (where the presence of the option means something) should
be specified with ``None``.
For example:
.. code-block:: python3
{'snes_monitor': None}
To use the ``pre_jacobian_callback`` or ``pre_function_callback``
functionality, the user-defined function must accept the current
solution as a petsc4py Vec. Example usage is given below:
.. code-block:: python3
def update_diffusivity(current_solution):
with cursol.dat.vec_wo as v:
current_solution.copy(v)
solve(trial*test*dx == dot(grad(cursol), grad(test))*dx, diffusivity)
solver = NonlinearVariationalSolver(problem,
pre_jacobian_callback=update_diffusivity)
"""
assert isinstance(problem, NonlinearVariationalProblem)
solver_parameters = solving_utils.set_defaults(
solver_parameters,
problem.J.arguments(),
ksp_defaults=self.DEFAULT_KSP_PARAMETERS,
snes_defaults=self.DEFAULT_SNES_PARAMETERS)
super().__init__(solver_parameters, options_prefix)
# Now the correct parameters live in self.parameters (via the
# OptionsManager mixin)
mat_type = self.parameters.get("mat_type")
pmat_type = self.parameters.get("pmat_type")
ctx = solving_utils._SNESContext(
problem,
mat_type=mat_type,
pmat_type=pmat_type,
appctx=appctx,
pre_jacobian_callback=pre_jacobian_callback,
pre_function_callback=pre_function_callback,
post_jacobian_callback=post_jacobian_callback,
post_function_callback=post_function_callback,
options_prefix=self.options_prefix)
self.snes = PETSc.SNES().create(comm=problem.dm.comm)
self._problem = problem
self._ctx = ctx
self._work = problem.u.dof_dset.layout_vec.duplicate()
self.snes.setDM(problem.dm)
ctx.set_function(self.snes)
ctx.set_jacobian(self.snes)
ctx.set_nullspace(nullspace,
problem.J.arguments()[0].function_space()._ises,
transpose=False,
near=False)
ctx.set_nullspace(transpose_nullspace,
problem.J.arguments()[1].function_space()._ises,
transpose=True,
near=False)
ctx.set_nullspace(near_nullspace,
problem.J.arguments()[0].function_space()._ises,
transpose=False,
near=True)
ctx._nullspace = nullspace
ctx._nullspace_T = transpose_nullspace
ctx._near_nullspace = near_nullspace
# Set from options now, so that people who want to noodle with
# the snes object directly (mostly Patrick), can. We need the
# DM with an app context in place so that if the DM is active
# on a subKSP the context is available.
dm = self.snes.getDM()
with dmhooks.add_hooks(dm, self, appctx=self._ctx, save=False):
self.set_from_options(self.snes)
# Used for custom grid transfer.
self._transfer_operators = ()
self._setup = False
def __init__(self, A, *, P=None, solver_parameters=None,
nullspace=None, transpose_nullspace=None,
near_nullspace=None, options_prefix=None):
"""A linear solver for assembled systems (Ax = b).
:arg A: a :class:`~.MatrixBase` (the operator).
:arg P: an optional :class:`~.MatrixBase` to construct any
preconditioner from; if none is supplied ``A`` is
used to construct the preconditioner.
:kwarg parameters: (optional) dict of solver parameters.
:kwarg nullspace: an optional :class:`~.VectorSpaceBasis` (or
:class:`~.MixedVectorSpaceBasis` spanning the null space
of the operator.
:kwarg transpose_nullspace: as for the nullspace, but used to
make the right hand side consistent.
:kwarg near_nullspace: as for the nullspace, but used to set
the near nullpace.
:kwarg options_prefix: an optional prefix used to distinguish
PETSc options. If not provided a unique prefix will be
created. Use this option if you want to pass options
to the solver from the command line in addition to
through the ``solver_parameters`` dict.
.. note::
Any boundary conditions for this solve *must* have been
applied when assembling the operator.
"""
if not isinstance(A, matrix.MatrixBase):
raise TypeError("Provided operator is a '%s', not a MatrixBase" % type(A).__name__)
if P is not None and not isinstance(P, matrix.MatrixBase):
raise TypeError("Provided preconditioner is a '%s', not a MatrixBase" % type(P).__name__)
solver_parameters = solving_utils.set_defaults(solver_parameters,
A.a.arguments(),
ksp_defaults=self.DEFAULT_KSP_PARAMETERS)
self.A = A
self.comm = A.comm
self.P = P if P is not None else A
# Set up parameters mixin
super().__init__(solver_parameters, options_prefix)
self.A.petscmat.setOptionsPrefix(self.options_prefix)
self.P.petscmat.setOptionsPrefix(self.options_prefix)
# If preconditioning matrix is matrix-free, then default to no
# preconditioning.
if isinstance(self.P, matrix.ImplicitMatrix):
self.set_default_parameter("pc_type", "none")
self.ksp = PETSc.KSP().create(comm=self.comm)
W = self.test_space
# DM provides fieldsplits (but not operators)
self.ksp.setDM(W.dm)
self.ksp.setDMActive(False)
if nullspace is not None:
nullspace._apply(self.A)
if P is not None:
nullspace._apply(self.P)
if transpose_nullspace is not None:
transpose_nullspace._apply(self.A, transpose=True)
if P is not None:
transpose_nullspace._apply(self.P, transpose=True)
if near_nullspace is not None:
near_nullspace._apply(self.A, near=True)
if P is not None:
near_nullspace._apply(self.P, near=True)
self.nullspace = nullspace
self.transpose_nullspace = transpose_nullspace
self.near_nullspace = near_nullspace
# Operator setting must come after null space has been
# applied
self.ksp.setOperators(A=self.A.petscmat, P=self.P.petscmat)
# Set from options now (we're not allowed to change parameters
# anyway).
self.set_from_options(self.ksp)
