from firedrake.petsc import PETSc
from firedrake.preconditioners.base import PCBase
import firedrake.dmhooks as dmhooks
__all__ = ['GTMGPC']
[docs]
class GTMGPC(PCBase):
needs_python_pmat = False
_prefix = "gt_"
[docs]
def initialize(self, pc):
from firedrake import TestFunction, parameters
from firedrake.assemble import get_assembler
from firedrake.interpolation import Interpolator
from firedrake.solving_utils import _SNESContext
from firedrake.matrix_free.operators import ImplicitMatrixContext
_, P = pc.getOperators()
appctx = self.get_appctx(pc)
fcp = appctx.get("form_compiler_parameters")
if pc.getType() != "python":
raise ValueError("Expecting PC type python")
ctx = dmhooks.get_appctx(pc.getDM())
if ctx is None:
raise ValueError("No context found.")
if not isinstance(ctx, _SNESContext):
raise ValueError("Don't know how to get form from %r" % ctx)
prefix = pc.getOptionsPrefix()
options_prefix = prefix + self._prefix
opts = PETSc.Options()
# Handle the fine operator if type is python
if P.getType() == "python":
ictx = P.getPythonContext()
if ictx is None:
raise ValueError("No context found on matrix")
if not isinstance(ictx, ImplicitMatrixContext):
raise ValueError("Don't know how to get form from %r" % ictx)
fine_operator = ictx.a
fine_bcs = ictx.row_bcs
if fine_bcs != ictx.col_bcs:
raise NotImplementedError("Row and column bcs must match")
fine_mat_type = opts.getString(options_prefix + "mat_type",
parameters["default_matrix_type"])
fine_form_assembler = get_assembler(fine_operator, bcs=fine_bcs, form_compiler_parameters=fcp, mat_type=fine_mat_type, options_prefix=options_prefix)
self.fine_op = fine_form_assembler.allocate()
self._assemble_fine_op = fine_form_assembler.assemble
self._assemble_fine_op(tensor=self.fine_op)
fine_petscmat = self.fine_op.petscmat
else:
fine_petscmat = P
# Transfer fine operator null space
fine_petscmat.setNullSpace(P.getNullSpace())
fine_transpose_nullspace = P.getTransposeNullSpace()
if fine_transpose_nullspace.handle != 0:
fine_petscmat.setTransposeNullSpace(fine_transpose_nullspace)
# Handle the coarse operator
coarse_options_prefix = options_prefix + "mg_coarse_"
coarse_mat_type = opts.getString(coarse_options_prefix + "mat_type",
parameters["default_matrix_type"])
get_coarse_space = appctx.get("get_coarse_space", None)
if not get_coarse_space:
raise ValueError("Need to provide a callback which provides the coarse space.")
coarse_space = get_coarse_space()
get_coarse_operator = appctx.get("get_coarse_operator", None)
if not get_coarse_operator:
raise ValueError("Need to provide a callback which provides the coarse operator.")
coarse_operator = get_coarse_operator()
coarse_space_bcs = appctx.get("coarse_space_bcs", None)
# These should be callbacks which return the relevant nullspaces
get_coarse_nullspace = appctx.get("get_coarse_op_nullspace", None)
get_coarse_transpose_nullspace = appctx.get("get_coarse_op_transpose_nullspace", None)
coarse_form_assembler = get_assembler(coarse_operator, bcs=coarse_space_bcs, form_compiler_parameters=fcp, mat_type=coarse_mat_type, options_prefix=coarse_options_prefix)
self.coarse_op = coarse_form_assembler.allocate()
self._assemble_coarse_op = coarse_form_assembler.assemble
self._assemble_coarse_op(tensor=self.coarse_op)
coarse_opmat = self.coarse_op.petscmat
# Set nullspace if provided
if get_coarse_nullspace:
nsp = get_coarse_nullspace()
coarse_opmat.setNullSpace(nsp.nullspace())
if get_coarse_transpose_nullspace:
tnsp = get_coarse_transpose_nullspace()
coarse_opmat.setTransposeNullSpace(tnsp.nullspace())
interp_petscmat = appctx.get("interpolation_matrix", None)
if interp_petscmat is None:
# Create interpolation matrix from coarse space to fine space
fine_space = ctx.J.arguments()[0].function_space()
interpolator = Interpolator(TestFunction(coarse_space), fine_space)
interpolation_matrix = interpolator.callable()
interp_petscmat = interpolation_matrix.handle
# We set up a PCMG object that uses the constructed interpolation
# matrix to generate the restriction/prolongation operators.
# This is a two-level multigrid preconditioner.
pcmg = PETSc.PC().create(comm=pc.comm)
pcmg.incrementTabLevel(1, parent=pc)
pcmg.setType(pc.Type.MG)
pcmg.setOptionsPrefix(options_prefix)
pcmg.setMGLevels(2)
pcmg.setMGCycleType(pc.MGCycleType.V)
pcmg.setMGInterpolation(1, interp_petscmat)
pcmg.setOperators(A=fine_petscmat, P=fine_petscmat)
coarse_solver = pcmg.getMGCoarseSolve()
coarse_solver.setOperators(A=coarse_opmat, P=coarse_opmat)
# coarse space dm
coarse_dm = coarse_space.dm
coarse_solver.setDM(coarse_dm)
coarse_solver.setDMActive(False)
pcmg.setDM(pc.getDM())
pcmg.setFromOptions()
self.pc = pcmg
self._dm = coarse_dm
prefix = coarse_solver.getOptionsPrefix()
# Create new appctx
self._ctx_ref = self.new_snes_ctx(pc,
coarse_operator,
coarse_space_bcs,
coarse_mat_type,
fcp,
options_prefix=prefix)
with dmhooks.add_hooks(coarse_dm, self,
appctx=self._ctx_ref,
save=False):
coarse_solver.setFromOptions()
[docs]
def update(self, pc):
if hasattr(self, "fine_op"):
self._assemble_fine_op(tensor=self.fine_op)
self._assemble_coarse_op(tensor=self.coarse_op)
self.pc.setUp()
[docs]
def apply(self, pc, X, Y):
dm = self._dm
with dmhooks.add_hooks(dm, self, appctx=self._ctx_ref):
self.pc.apply(X, Y)
[docs]
def applyTranspose(self, pc, X, Y):
dm = self._dm
with dmhooks.add_hooks(dm, self, appctx=self._ctx_ref):
self.pc.applyTranspose(X, Y)
[docs]
def view(self, pc, viewer=None):
super(GTMGPC, self).view(pc, viewer)
if hasattr(self, "pc"):
viewer.printfASCII("PC using Gopalakrishnan and Tan algorithm\n")
self.pc.view(viewer)
