Source code for pymor.reductors.residual

# This file is part of the pyMOR project (http://www.pymor.org).

import numpy as np

from pymor.algorithms.image import estimate_image_hierarchical
from pymor.algorithms.projection import project, project_to_subbasis
from pymor.core.interfaces import BasicInterface
from pymor.core.exceptions import ImageCollectionError
from pymor.operators.basic import OperatorBase
from pymor.operators.constructions import induced_norm

[docs]class ResidualReductor(BasicInterface): """Generic reduced basis residual reductor. Given an operator and a right-hand side, the residual is given by:: residual.apply(U, mu) == operator.apply(U, mu) - rhs.as_vector(mu) When the rhs is a functional we are interested in the Riesz representative of the residual:: residual.apply(U, mu) == product.apply_inverse(operator.apply(U, mu) - rhs.as_vector(mu)) Given a basis `RB` of a subspace of the source space of `operator`, this reductor uses :func:`~pymor.algorithms.image.estimate_image_hierarchical` to determine a low-dimensional subspace containing the image of the subspace under `residual` (resp. `riesz_residual`), computes an orthonormal basis `residual_range` for this range space and then returns the Petrov-Galerkin projection :: projected_residual == project(residual, range_basis=residual_range, source_basis=RB) of the residual operator. Given a reduced basis coefficient vector `u`, w.r.t. `RB`, the (dual) norm of the residual can then be computed as :: projected_residual.apply(u, mu).l2_norm() Moreover, a `reconstruct` method is provided such that :: residual_reductor.reconstruct(projected_residual.apply(u, mu)) == residual.apply(RB.lincomb(u), mu) Parameters ---------- RB |VectorArray| containing a basis of the reduced space onto which to project. operator See definition of `residual`. rhs See definition of `residual`. If `None`, zero right-hand side is assumed. product Inner product |Operator| w.r.t. which to orthonormalize and w.r.t. which to compute the Riesz representatives in case `rhs` is a functional. """ def __init__(self, RB, operator, rhs=None, product=None): assert RB in operator.source assert rhs is None \ or (rhs.range.is_scalar and rhs.source == operator.range and rhs.linear) \ or (rhs.source.is_scalar and rhs.range == operator.range and rhs.linear) assert product is None or product.source == product.range == operator.range self.RB = RB self.operator = operator self.rhs = rhs self.product = product self.residual_range = operator.range.empty() self.residual_range_dims = [] def reduce(self): # Note that it is possible that rhs.source == rhs.range, nameley if both # are one-dimensional NumpyVectorSpaces which agree with the range of # operator. Usually, this should not happen, since at least one of these # spaces should have an id which is different from the id of operator.range. # However, even if it happens but rhs is actually a vector, we are on # the safe side, since first computing the Riesz representatives does not # change anything in one-dimensional spaces, and it does not matter whether # we project from the left or from the right. rhs_is_functional = (self.rhs.source == self.operator.range) if self.residual_range is not False: with self.logger.block('Estimating residual range ...'): try: self.residual_range, self.residual_range_dims = \ estimate_image_hierarchical([self.operator], [self.rhs.T if rhs_is_functional else self.rhs], self.RB, (self.residual_range, self.residual_range_dims), orthonormalize=True, product=self.product, riesz_representatives=rhs_is_functional) except ImageCollectionError as e: self.logger.warning('Cannot compute range of {}. Evaluation will be slow.'.format(e.op)) self.residual_range = False if self.residual_range is False: operator = project(self.operator, None, self.RB) return NonProjectedResidualOperator(operator, self.rhs, rhs_is_functional, self.product) with self.logger.block('Projecting residual operator ...'): if rhs_is_functional: operator = project(self.operator, self.residual_range, self.RB, product=None) # the product cancels out. rhs = project(self.rhs, None, self.residual_range, product=None) else: operator = project(self.operator, self.residual_range, self.RB, product=self.product) rhs = project(self.rhs, self.residual_range, None, product=self.product) return ResidualOperator(operator, rhs, rhs_is_functional)
[docs] def reconstruct(self, u): """Reconstruct high-dimensional residual vector from reduced vector `u`.""" if self.residual_range is False: if self.product: norm = induced_norm(self.product) return u * (u.l2_norm() / norm(u))[0] else: return u else: return self.residual_range[:u.dim].lincomb(u.to_numpy())
[docs]class ResidualOperator(OperatorBase): """Instantiated by :class:`ResidualReductor`.""" def __init__(self, operator, rhs, rhs_is_functional=True, name=None): self.source = operator.source self.range = operator.range self.linear = operator.linear self.operator = operator self.rhs = rhs self.rhs_vector = rhs.as_vector(space=operator.range) if rhs and not rhs.parametric else None self.rhs_is_functional = rhs_is_functional self.name = name
[docs] def apply(self, U, mu=None): V = self.operator.apply(U, mu=mu) if self.rhs: F = self.rhs_vector or self.rhs.as_vector(mu, space=self.operator.range) if len(V) > 1: V -= F[[0]*len(V)] else: V -= F return V
def projected_to_subbasis(self, dim_range=None, dim_source=None, name=None): if self.rhs_is_functional: rhs = project_to_subbasis(self.rhs, None, dim_range) else: rhs = project_to_subbasis(self.rhs, dim_range, None) return ResidualOperator(project_to_subbasis(self.operator, dim_range, dim_source), rhs, self.rhs_is_functional, name=name)
[docs]class NonProjectedResidualOperator(ResidualOperator): """Instantiated by :class:`ResidualReductor`. Not to be used directly. """ def __init__(self, operator, rhs, rhs_is_functional, product): super().__init__(operator, rhs, rhs_is_functional) self.product = product
[docs] def apply(self, U, mu=None): R = super().apply(U, mu=mu) if self.product: if self.rhs_is_functional: R_riesz = self.product.apply_inverse(R) return R_riesz * (np.sqrt(R_riesz.dot(R)) / R_riesz.l2_norm())[0] else: return R * (np.sqrt(self.product.pairwise_apply2(R, R)) / R.l2_norm())[0] else: return R
def projected_to_subbasis(self, dim_range=None, dim_source=None, name=None): return self.with_(operator=project_to_subbasis(self.operator, None, dim_source))
[docs]class ImplicitEulerResidualReductor(BasicInterface): """Reduced basis residual reductor with mass operator for implicit Euler timestepping. Given an operator, mass and a functional, the concatenation of residual operator with the Riesz isomorphism is given by:: riesz_residual.apply(U, U_old, mu) == product.apply_inverse(operator.apply(U, mu) + 1/dt*mass.apply(U, mu) - 1/dt*mass.apply(U_old, mu) - functional.as_vector(mu)) This reductor determines a low-dimensional subspace of the image of a reduced basis space under `riesz_residual` using :func:`~pymor.algorithms.image.estimate_image_hierarchical`, computes an orthonormal basis `residual_range` of this range space and then returns the Petrov-Galerkin projection :: projected_riesz_residual == riesz_residual.projected(range_basis=residual_range, source_basis=RB) of the `riesz_residual` operator. Given reduced basis coefficient vectors `u` and `u_old`, the dual norm of the residual can then be computed as :: projected_riesz_residual.apply(u, u_old, mu).l2_norm() Moreover, a `reconstruct` method is provided such that :: residual_reductor.reconstruct(projected_riesz_residual.apply(u, u_old, mu)) == riesz_residual.apply(RB.lincomb(u), RB.lincomb(u_old), mu) Parameters ---------- operator See definition of `riesz_residual`. mass The mass operator. See definition of `riesz_residual`. dt The time step size. See definition of `riesz_residual`. functional See definition of `riesz_residual`. If `None`, zero right-hand side is assumed. RB |VectorArray| containing a basis of the reduced space onto which to project. product Inner product |Operator| w.r.t. which to compute the Riesz representatives. """ def __init__(self, RB, operator, mass, dt, functional=None, product=None): assert RB in operator.source assert functional is None \ or functional.range.is_scalar and functional.source == operator.source and functional.linear assert product is None or product.source == product.range == operator.range self.RB = RB self.operator = operator self.mass = mass self.dt = dt self.functional = functional self.product = product self.residual_range = operator.range.empty() self.residual_range_dims = [] def reduce(self): if self.residual_range is not False: with self.logger.block('Estimating residual range ...'): try: self.residual_range, self.residual_range_dims = \ estimate_image_hierarchical([self.operator, self.mass], [self.functional.T], self.RB, (self.residual_range, self.residual_range_dims), orthonormalize=True, product=self.product, riesz_representatives=True) except ImageCollectionError as e: self.logger.warning('Cannot compute range of {}. Evaluation will be slow.'.format(e.op)) self.residual_range = False if self.residual_range is False: operator = project(self.operator, None, self.RB) mass = project(self.mass, None, self.RB) return NonProjectedImplicitEulerResidualOperator(operator, mass, self.functional, self.dt, self.product) with self.logger.block('Projecting residual operator ...'): operator = project(self.operator, self.residual_range, self.RB, product=None) # the product always cancels out. mass = project(self.mass, self.residual_range, self.RB, product=None) functional = project(self.functional, None, self.residual_range, product=None) return ImplicitEulerResidualOperator(operator, mass, functional, self.dt)
[docs] def reconstruct(self, u): """Reconstruct high-dimensional residual vector from reduced vector `u`.""" if self.residual_range is False: if self.product: norm = induced_norm(self.product) return u * (u.l2_norm() / norm(u))[0] else: return u else: return self.residual_range[:u.dim].lincomb(u.to_numpy())
[docs]class ImplicitEulerResidualOperator(OperatorBase): """Instantiated by :class:`ImplicitEulerResidualReductor`.""" def __init__(self, operator, mass, functional, dt, name=None): self.source = operator.source self.range = operator.range self.linear = operator.linear self.operator = operator self.mass = mass self.functional = functional self.functional_vector = functional.as_source_array() if functional and not functional.parametric else None self.dt = dt self.name = name
[docs] def apply(self, U, U_old, mu=None): V = self.operator.apply(U, mu=mu) V.axpy(1./self.dt, self.mass.apply(U, mu=mu)) V.axpy(-1./self.dt, self.mass.apply(U_old, mu=mu)) if self.functional: F = self.functional_vector or self.functional.as_source_array(mu) if len(V) > 1: V -= F[[0]*len(V)] else: V -= F return V
def projected_to_subbasis(self, dim_range=None, dim_source=None, name=None): return ImplicitEulerResidualOperator(project_to_subbasis(self.operator, dim_range, dim_source), project_to_subbasis(self.mass, dim_range, dim_source), project_to_subbasis(self.functional, None, dim_range), self.dt, name=name)
[docs]class NonProjectedImplicitEulerResidualOperator(ImplicitEulerResidualOperator): """Instantiated by :class:`ImplicitEulerResidualReductor`. Not to be used directly. """ def __init__(self, operator, mass, functional, dt, product): super().__init__(operator, mass, functional, dt) self.product = product
[docs] def apply(self, U, U_old, mu=None): R = super().apply(U, U_old, mu=mu) if self.product: R_riesz = self.product.apply_inverse(R) return R_riesz * (np.sqrt(R_riesz.pairwise_dot(R)) / R_riesz.l2_norm())[0] else: return R
def projected_to_subbasis(self, dim_range=None, dim_source=None, name=None): return self.with_(operator=project_to_subbasis(self.operator, None, dim_source), mass=project_to_subbasis(self.mass, None, dim_source))