Source code for pymordemos.parabolic_mor

#!/usr/bin/env python
# This file is part of the pyMOR project (http://www.pymor.org).

"""Reduced basis approximation of the heat equation.

Usage:
parabolic_mor.py BACKEND ALG SNAPSHOTS RBSIZE TEST

Arguments:
BACKEND    Discretization toolkit to use (pymor, fenics).
ALG        The model reduction algorithm to use
SNAPSHOTS  greedy/pod:      number of training set parameters
RBSIZE     Size of the reduced basis.
TEST       Number of test parameters for reduction error estimation.
"""

from functools import partial    # fix parameters of given function

import numpy as np

from pymor.basic import *        # most common pyMOR functions and classes
from pymor.algorithms.timestepping import ImplicitEulerTimeStepper

# parameters for high-dimensional models
GRID_INTERVALS = 100
FENICS_ORDER = 2
NT = 100
DT = 1. / NT

####################################################################################################
# High-dimensional models                                                                          #
####################################################################################################

[docs]def discretize_pymor(): # setup analytical problem problem = InstationaryProblem( StationaryProblem( domain=RectDomain(top='dirichlet', bottom='neumann'), diffusion=LincombFunction( [ConstantFunction(1., dim_domain=2), ExpressionFunction('(x[..., 0] > 0.45) * (x[..., 0] < 0.55) * (x[..., 1] < 0.7) * 1.', dim_domain=2), ExpressionFunction('(x[..., 0] > 0.35) * (x[..., 0] < 0.40) * (x[..., 1] > 0.3) * 1. + ' '(x[..., 0] > 0.60) * (x[..., 0] < 0.65) * (x[..., 1] > 0.3) * 1.', dim_domain=2)], [1., 100. - 1., ExpressionParameterFunctional('top - 1.', {'top': 0})] ), rhs=ConstantFunction(value=100., dim_domain=2) * ExpressionParameterFunctional('sin(10*pi*_t)', {'_t': ()}), dirichlet_data=ConstantFunction(value=0., dim_domain=2), neumann_data=ExpressionFunction('(x[..., 0] > 0.45) * (x[..., 0] < 0.55) * -1000.', dim_domain=2), ), T=1., initial_data=ExpressionFunction('(x[..., 0] > 0.45) * (x[..., 0] < 0.55) * (x[..., 1] < 0.7) * 10.', dim_domain=2), parameter_space=CubicParameterSpace({'top': 0}, minimum=1, maximum=100.) ) # discretize using continuous finite elements fom, _ = discretize_instationary_cg(analytical_problem=problem, diameter=1./GRID_INTERVALS, nt=NT) fom.enable_caching('disk') return fom
[docs]def discretize_fenics(): from pymor.tools import mpi if mpi.parallel: from pymor.models.mpi import mpi_wrap_model return mpi_wrap_model(_discretize_fenics, use_with=True, pickle_local_spaces=False) else: return _discretize_fenics()
def _discretize_fenics(): # assemble system matrices - FEniCS code ######################################## import dolfin as df # discrete function space mesh = df.UnitSquareMesh(GRID_INTERVALS, GRID_INTERVALS, 'crossed') V = df.FunctionSpace(mesh, 'Lagrange', FENICS_ORDER) u = df.TrialFunction(V) v = df.TestFunction(V) # data functions bottom_diffusion = df.Expression('(x[0] > 0.45) * (x[0] < 0.55) * (x[1] < 0.7) * 1.', element=df.FunctionSpace(mesh, 'DG', 0).ufl_element()) top_diffusion = df.Expression('(x[0] > 0.35) * (x[0] < 0.40) * (x[1] > 0.3) * 1. +' '(x[0] > 0.60) * (x[0] < 0.65) * (x[1] > 0.3) * 1.', element=df.FunctionSpace(mesh, 'DG', 0).ufl_element()) initial_data = df.Expression('(x[0] > 0.45) * (x[0] < 0.55) * (x[1] < 0.7) * 10.', element=df.FunctionSpace(mesh, 'DG', 0).ufl_element()) neumann_data = df.Expression('(x[0] > 0.45) * (x[0] < 0.55) * 1000.', element=df.FunctionSpace(mesh, 'DG', 0).ufl_element()) # assemble matrices and vectors l2_mat = df.assemble(df.inner(u, v) * df.dx) l2_0_mat = l2_mat.copy() h1_mat = df.assemble(df.inner(df.nabla_grad(u), df.nabla_grad(v)) * df.dx) h1_0_mat = h1_mat.copy() mat0 = h1_mat.copy() mat0.zero() bottom_mat = df.assemble(bottom_diffusion * df.inner(df.nabla_grad(u), df.nabla_grad(v)) * df.dx) top_mat = df.assemble(top_diffusion * df.inner(df.nabla_grad(u), df.nabla_grad(v)) * df.dx) u0 = df.project(initial_data, V).vector() f = df.assemble(neumann_data * v * df.ds) # boundary treatment def dirichlet_boundary(x, on_boundary): tol = 1e-14 return on_boundary and (abs(x[0]) < tol or abs(x[0] - 1) < tol or abs(x[1] - 1) < tol) bc = df.DirichletBC(V, df.Constant(0.), dirichlet_boundary) bc.apply(l2_0_mat) bc.apply(h1_0_mat) bc.apply(mat0) bc.zero(bottom_mat) bc.zero(top_mat) bc.apply(f) bc.apply(u0) # wrap everything as a pyMOR model ################################## from pymor.bindings.fenics import FenicsVectorSpace, FenicsMatrixOperator, FenicsVisualizer fom = InstationaryModel( T=1., initial_data=FenicsVectorSpace(V).make_array([u0]), operator=LincombOperator([FenicsMatrixOperator(mat0, V, V), FenicsMatrixOperator(h1_0_mat, V, V), FenicsMatrixOperator(bottom_mat, V, V), FenicsMatrixOperator(top_mat, V, V)], [1., 1., 100. - 1., ExpressionParameterFunctional('top - 1.', {'top': 0})]), rhs=VectorOperator(FenicsVectorSpace(V).make_array([f])), mass=FenicsMatrixOperator(l2_0_mat, V, V, name='l2'), products={'l2': FenicsMatrixOperator(l2_mat, V, V, name='l2'), 'l2_0': FenicsMatrixOperator(l2_0_mat, V, V, name='l2_0'), 'h1': FenicsMatrixOperator(h1_mat, V, V, name='h1'), 'h1_0_semi': FenicsMatrixOperator(h1_0_mat, V, V, name='h1_0_semi')}, time_stepper=ImplicitEulerTimeStepper(nt=NT), parameter_space=CubicParameterSpace({'top': 0}, minimum=1, maximum=100.), visualizer=FenicsVisualizer(FenicsVectorSpace(V)) ) return fom #################################################################################################### # Reduction algorithms # ####################################################################################################
[docs]def reduce_greedy(fom, reductor, snapshots, basis_size): training_set = fom.parameter_space.sample_uniformly(snapshots) pool = new_parallel_pool() greedy_data = rb_greedy(fom, reductor, training_set, max_extensions=basis_size, pool=pool) return greedy_data['rom']
[docs]def reduce_adaptive_greedy(fom, reductor, validation_mus, basis_size): pool = new_parallel_pool() greedy_data = rb_adaptive_greedy(fom, reductor, validation_mus=validation_mus, max_extensions=basis_size, pool=pool) return greedy_data['rom']
[docs]def reduce_pod(fom, reductor, snapshots, basis_size): training_set = fom.parameter_space.sample_uniformly(snapshots) snapshots = fom.operator.source.empty() for mu in training_set: snapshots.append(fom.solve(mu)) basis, singular_values = pod(snapshots, modes=basis_size, product=fom.h1_0_semi_product) reductor.extend_basis(basis, method='trivial') rom = reductor.reduce() return rom
#################################################################################################### # Main script # ####################################################################################################
[docs]def main(BACKEND, ALG, SNAPSHOTS, RBSIZE, TEST): # discretize ############ if BACKEND == 'pymor': fom = discretize_pymor() elif BACKEND == 'fenics': fom = discretize_fenics() else: raise NotImplementedError # select reduction algorithm with error estimator ################################################# coercivity_estimator = ExpressionParameterFunctional('1.', fom.parameter_type) reductor = ParabolicRBReductor(fom, product=fom.h1_0_semi_product, coercivity_estimator=coercivity_estimator) # generate reduced model ######################## if ALG == 'greedy': rom = reduce_greedy(fom, reductor, SNAPSHOTS, RBSIZE) elif ALG == 'adaptive_greedy': rom = reduce_adaptive_greedy(fom, reductor, SNAPSHOTS, RBSIZE) elif ALG == 'pod': rom = reduce_pod(fom, reductor, SNAPSHOTS, RBSIZE) else: raise NotImplementedError # evaluate the reduction error ############################## results = reduction_error_analysis( rom, fom=fom, reductor=reductor, estimator=True, error_norms=[lambda U: DT * np.sqrt(np.sum(fom.h1_0_semi_norm(U)[1:]**2))], error_norm_names=['l^2-h^1'], condition=False, test_mus=TEST, random_seed=999, plot=True ) # show results ############## print(results['summary']) import matplotlib.pyplot as plt plt.show(results['figure']) # write results to disk ####################### from pymor.core.pickle import dump dump(rom, open('reduced_model.out', 'wb')) results.pop('figure') # matplotlib figures cannot be serialized dump(results, open('results.out', 'wb')) # visualize reduction error for worst-approximated mu ##################################################### mumax = results['max_error_mus'][0, -1] U = fom.solve(mumax) U_RB = reductor.reconstruct(rom.solve(mumax)) if BACKEND == 'fenics': # right now the fenics visualizer does not support time trajectories U = U[len(U) - 1].copy() U_RB = U_RB[len(U_RB) - 1].copy() fom.visualize((U, U_RB, U - U_RB), legend=('Detailed Solution', 'Reduced Solution', 'Error'), separate_colorbars=True) return results
if __name__ == '__main__': import sys if len(sys.argv) != 6: print(__doc__) sys.exit(1) BACKEND, ALG, SNAPSHOTS, RBSIZE, TEST = sys.argv[1:] BACKEND, ALG, SNAPSHOTS, RBSIZE, TEST = BACKEND.lower(), ALG.lower(), int(SNAPSHOTS), int(RBSIZE), int(TEST) main(BACKEND, ALG, SNAPSHOTS, RBSIZE, TEST)