--- /dev/null
+/* ---------------------------------------------------------------------
+ *
+ * Copyright (C) 2003 - 2018 by the deal.II authors
+ *
+ * This file is part of the deal.II library.
+ *
+ * The deal.II library is free software; you can use it, redistribute
+ * it, and/or modify it under the terms of the GNU Lesser General
+ * Public License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ * The full text of the license can be found in the file LICENSE.md at
+ * the top level directory of deal.II.
+ *
+ * ---------------------------------------------------------------------
+ *
+ * Authors: Thomas Clevenger, Clemson University
+ * Timo Heister, University of Utah
+ */
+
+// @note: This is work in progress and will be an example for block smoothers
+// in geometric multigrid. For now, this is just step-16.
+
+// @sect3{Include files}
+
+// Again, the first few include files are already known, so we won't comment
+// on them:
+#include <deal.II/base/quadrature_lib.h>
+#include <deal.II/base/function.h>
+#include <deal.II/base/logstream.h>
+#include <deal.II/base/utilities.h>
+
+#include <deal.II/lac/affine_constraints.h>
+#include <deal.II/lac/vector.h>
+#include <deal.II/lac/full_matrix.h>
+#include <deal.II/lac/sparse_matrix.h>
+#include <deal.II/lac/solver_cg.h>
+#include <deal.II/lac/precondition.h>
+
+#include <deal.II/grid/tria.h>
+#include <deal.II/grid/tria_accessor.h>
+#include <deal.II/grid/tria_iterator.h>
+#include <deal.II/grid/grid_generator.h>
+#include <deal.II/grid/grid_refinement.h>
+
+#include <deal.II/dofs/dof_accessor.h>
+#include <deal.II/dofs/dof_tools.h>
+
+#include <deal.II/fe/fe_q.h>
+#include <deal.II/fe/fe_values.h>
+
+#include <deal.II/numerics/vector_tools.h>
+#include <deal.II/numerics/data_out.h>
+#include <deal.II/numerics/error_estimator.h>
+
+// These, now, are the include necessary for the multilevel methods. The first
+// one declares how to handle Dirichlet boundary conditions on each of the
+// levels of the multigrid method. For the actual description of the degrees
+// of freedom, we do not need any new include file because DoFHandler already
+// has all necessary methods implemented. We will only need to distribute the
+// DoFs for the levels further down.
+//
+// The rest of the include files deals with the mechanics of multigrid as a
+// linear operator (solver or preconditioner).
+#include <deal.II/multigrid/mg_constrained_dofs.h>
+#include <deal.II/multigrid/multigrid.h>
+#include <deal.II/multigrid/mg_transfer.h>
+#include <deal.II/multigrid/mg_tools.h>
+#include <deal.II/multigrid/mg_coarse.h>
+#include <deal.II/multigrid/mg_smoother.h>
+#include <deal.II/multigrid/mg_matrix.h>
+
+// We will be using MeshWorker::mesh_loop to loop over the cells, so include it
+// here:
+#include <deal.II/meshworker/mesh_loop.h>
+
+
+// This is C++:
+#include <iostream>
+#include <fstream>
+
+using namespace dealii;
+
+namespace Step16
+{
+ // @sect3{The Scratch and Copy objects}
+ //
+ // We use MeshWorker::mesh_loop() to assemble our matrices. For this, we
+ // need a ScratchData object to store temporary data on each cell (this is
+ // just the FEValues object) and a CopyData object that will contain the
+ // output of each cell assembly. For more details about the usage of scratch
+ // and copy objects, see the WorkStream namespace.
+ template <int dim>
+ struct ScratchData
+ {
+ ScratchData(const Mapping<dim> & mapping,
+ const FiniteElement<dim> &fe,
+ const unsigned int quadrature_degree,
+ const UpdateFlags update_flags)
+ : fe_values(mapping, fe, QGauss<dim>(quadrature_degree), update_flags)
+ {}
+
+ ScratchData(const ScratchData<dim> &scratch_data)
+ : fe_values(scratch_data.fe_values.get_mapping(),
+ scratch_data.fe_values.get_fe(),
+ scratch_data.fe_values.get_quadrature(),
+ scratch_data.fe_values.get_update_flags())
+ {}
+
+ FEValues<dim> fe_values;
+ };
+
+ struct CopyData
+ {
+ unsigned int level;
+ FullMatrix<double> cell_matrix;
+ Vector<double> cell_rhs;
+ std::vector<types::global_dof_index> local_dof_indices;
+
+ template <class Iterator>
+ void reinit(const Iterator &cell, unsigned int dofs_per_cell)
+ {
+ cell_matrix.reinit(dofs_per_cell, dofs_per_cell);
+ cell_rhs.reinit(dofs_per_cell);
+
+ local_dof_indices.resize(dofs_per_cell);
+ cell->get_active_or_mg_dof_indices(local_dof_indices);
+ level = cell->level();
+ }
+ };
+
+ // @sect3{The <code>LaplaceProblem</code> class template}
+
+ // This main class is similar to the same class in step-6. As far as
+ // member functions is concerned, the only additions are:
+ // - The <code>assemble_multigrid</code> function that assembles the matrices
+ // that correspond to the discrete operators on intermediate levels.
+ // - The <code>cell_worker</code> function that assembles our PDE on a single
+ // cell.
+ template <int dim>
+ class LaplaceProblem
+ {
+ public:
+ LaplaceProblem(const unsigned int degree);
+ void run();
+
+ private:
+ template <class Iterator>
+ void cell_worker(const Iterator & cell,
+ ScratchData<dim> &scratch_data,
+ CopyData & copy_data);
+
+ void setup_system();
+ void assemble_system();
+ void assemble_multigrid();
+ void solve();
+ void refine_grid();
+ void output_results(const unsigned int cycle) const;
+
+ Triangulation<dim> triangulation;
+ FE_Q<dim> fe;
+ DoFHandler<dim> dof_handler;
+
+ SparsityPattern sparsity_pattern;
+ SparseMatrix<double> system_matrix;
+
+ AffineConstraints<double> constraints;
+
+ Vector<double> solution;
+ Vector<double> system_rhs;
+
+ const unsigned int degree;
+
+ // The following members are the essential data structures for the multigrid
+ // method. The first four represent the sparsity patterns and the matrices
+ // on individual levels of the multilevel hierarchy, very much like the
+ // objects for the global mesh above.
+ //
+ // Then we have two new matrices only needed for multigrid methods with
+ // local smoothing on adaptive meshes. They convey data between the interior
+ // part of the refined region and the refinement edge, as outlined in detail
+ // in the @ref mg_paper "multigrid paper".
+ //
+ // The last object stores information about the boundary indices on each
+ // level and information about indices lying on a refinement edge between
+ // two different refinement levels. It thus serves a similar purpose as
+ // AffineConstraints, but on each level.
+ MGLevelObject<SparsityPattern> mg_sparsity_patterns;
+ MGLevelObject<SparsityPattern> mg_interface_sparsity_patterns;
+
+ MGLevelObject<SparseMatrix<double>> mg_matrices;
+ MGLevelObject<SparseMatrix<double>> mg_interface_matrices;
+ MGConstrainedDoFs mg_constrained_dofs;
+ };
+
+
+ // @sect3{The <code>LaplaceProblem</code> class implementation}
+
+ // Just one short remark about the constructor of the Triangulation:
+ // by convention, all adaptively refined triangulations in deal.II never
+ // change by more than one level across a face between cells. For our
+ // multigrid algorithms, however, we need a slightly stricter guarantee,
+ // namely that the mesh also does not change by more than refinement level
+ // across vertices that might connect two cells. In other words, we must
+ // prevent the following situation:
+ //
+ // @image html limit_level_difference_at_vertices.png ""
+ //
+ // This is achieved by passing the
+ // Triangulation::limit_level_difference_at_vertices flag to the constructor
+ // of the triangulation class.
+ template <int dim>
+ LaplaceProblem<dim>::LaplaceProblem(const unsigned int degree)
+ : triangulation(Triangulation<dim>::limit_level_difference_at_vertices)
+ , fe(degree)
+ , dof_handler(triangulation)
+ , degree(degree)
+ {}
+
+
+
+ // @sect4{LaplaceProblem::setup_system}
+
+ // In addition to just distributing the degrees of freedom in
+ // the DoFHandler, we do the same on each level. Then, we follow the
+ // same procedure as before to set up the system on the leaf mesh.
+ template <int dim>
+ void LaplaceProblem<dim>::setup_system()
+ {
+ dof_handler.distribute_dofs(fe);
+ dof_handler.distribute_mg_dofs();
+
+ std::cout << " Number of degrees of freedom: " << dof_handler.n_dofs()
+ << " (by level: ";
+ for (unsigned int level = 0; level < triangulation.n_levels(); ++level)
+ std::cout << dof_handler.n_dofs(level)
+ << (level == triangulation.n_levels() - 1 ? ")" : ", ");
+ std::cout << std::endl;
+
+
+ solution.reinit(dof_handler.n_dofs());
+ system_rhs.reinit(dof_handler.n_dofs());
+
+ constraints.clear();
+ DoFTools::make_hanging_node_constraints(dof_handler, constraints);
+
+ std::set<types::boundary_id> dirichlet_boundary_ids = {0};
+ Functions::ZeroFunction<dim> homogeneous_dirichlet_bc;
+ const std::map<types::boundary_id, const Function<dim> *>
+ dirichlet_boundary_functions = {
+ {types::boundary_id(0), &homogeneous_dirichlet_bc}};
+ VectorTools::interpolate_boundary_values(dof_handler,
+ dirichlet_boundary_functions,
+ constraints);
+ constraints.close();
+
+ {
+ DynamicSparsityPattern dsp(dof_handler.n_dofs(), dof_handler.n_dofs());
+ DoFTools::make_sparsity_pattern(dof_handler, dsp, constraints);
+ sparsity_pattern.copy_from(dsp);
+ }
+ system_matrix.reinit(sparsity_pattern);
+
+ // The multigrid constraints have to be initialized. They need to know
+ // where Dirichlet boundary conditions are prescribed.
+ mg_constrained_dofs.clear();
+ mg_constrained_dofs.initialize(dof_handler);
+ mg_constrained_dofs.make_zero_boundary_constraints(dof_handler,
+ dirichlet_boundary_ids);
+
+
+ // Now for the things that concern the multigrid data structures. First, we
+ // resize the multilevel objects to hold matrices and sparsity patterns for
+ // every level. The coarse level is zero (this is mandatory right now but
+ // may change in a future revision). Note that these functions take a
+ // complete, inclusive range here (not a starting index and size), so the
+ // finest level is <code>n_levels-1</code>. We first have to resize the
+ // container holding the SparseMatrix classes, since they have to release
+ // their SparsityPattern before the can be destroyed upon resizing.
+ const unsigned int n_levels = triangulation.n_levels();
+
+ mg_interface_matrices.resize(0, n_levels - 1);
+ mg_matrices.resize(0, n_levels - 1);
+ mg_sparsity_patterns.resize(0, n_levels - 1);
+ mg_interface_sparsity_patterns.resize(0, n_levels - 1);
+
+ // Now, we have to provide a matrix on each level. To this end, we first use
+ // the MGTools::make_sparsity_pattern function to generate a preliminary
+ // compressed sparsity pattern on each level (see the @ref Sparsity module
+ // for more information on this topic) and then copy it over to the one we
+ // really want. The next step is to initialize the interface matrices with
+ // the fitting sparsity pattern.
+ //
+ // It may be worth pointing out that the interface matrices only have
+ // entries for degrees of freedom that sit at or next to the interface
+ // between coarser and finer levels of the mesh. They are therefore even
+ // sparser than the matrices on the individual levels of our multigrid
+ // hierarchy. Therefore, we use a function specifically build for this
+ // purpose to generate it.
+ for (unsigned int level = 0; level < n_levels; ++level)
+ {
+ {
+ DynamicSparsityPattern dsp(dof_handler.n_dofs(level),
+ dof_handler.n_dofs(level));
+ MGTools::make_sparsity_pattern(dof_handler, dsp, level);
+
+ mg_sparsity_patterns[level].copy_from(dsp);
+ mg_matrices[level].reinit(mg_sparsity_patterns[level]);
+ }
+ {
+ DynamicSparsityPattern dsp(dof_handler.n_dofs(level),
+ dof_handler.n_dofs(level));
+ MGTools::make_interface_sparsity_pattern(dof_handler,
+ mg_constrained_dofs,
+ dsp,
+ level);
+ mg_interface_sparsity_patterns[level].copy_from(dsp);
+ mg_interface_matrices[level].reinit(
+ mg_interface_sparsity_patterns[level]);
+ }
+ }
+ }
+
+
+ // @sect4{LaplaceProblem::cell_worker}
+
+ // The cell_worker function is used to assemble the matrix and right-hand side
+ // on the given cell. This function is used for the active cells to generate
+ // the system_matrix and on each level to build the level matrices.
+ //
+ // Note that we also assemble a right-hand side when called from
+ // assemble_multigrid() even though it is not used.
+ template <int dim>
+ template <class Iterator>
+ void LaplaceProblem<dim>::cell_worker(const Iterator & cell,
+ ScratchData<dim> &scratch_data,
+ CopyData & copy_data)
+ {
+ FEValues<dim> &fe_values = scratch_data.fe_values;
+ fe_values.reinit(cell);
+
+ const unsigned int dofs_per_cell = fe_values.get_fe().dofs_per_cell;
+ const unsigned int n_q_points = fe_values.get_quadrature().size();
+
+ copy_data.reinit(cell, dofs_per_cell);
+
+ const std::vector<double> &JxW = fe_values.get_JxW_values();
+
+ for (unsigned int q = 0; q < n_q_points; ++q)
+ {
+ const double coefficient =
+ (fe_values.get_quadrature_points()[q][0] < 0.0) ? 1.0 : 0.1;
+ //(cell->center().square() < 0.5 * 0.5) ? 10.0:1.0;
+
+ for (unsigned int i = 0; i < dofs_per_cell; ++i)
+ {
+ for (unsigned int j = 0; j < dofs_per_cell; ++j)
+ {
+ copy_data.cell_matrix(i, j) +=
+ coefficient *
+ (fe_values.shape_grad(i, q) * fe_values.shape_grad(j, q)) *
+ JxW[q];
+ }
+ copy_data.cell_rhs(i) += 1.0 * fe_values.shape_value(i, q) * JxW[q];
+ }
+ }
+ }
+
+
+
+ // @sect4{LaplaceProblem::assemble_system}
+
+ // The following function assembles the linear system on the active cells of
+ // the mesh. For this, we pass two lambda functions to the mesh_loop()
+ // function. The cell_worker function redirects to the class member function
+ // of the same name, while the copier is specific to this function and copies
+ // local matrix and vector to the corresponding global ones using the
+ // constraints.
+ template <int dim>
+ void LaplaceProblem<dim>::assemble_system()
+ {
+ MappingQ1<dim> mapping;
+
+ auto cell_worker =
+ [&](const typename DoFHandler<dim>::active_cell_iterator &cell,
+ ScratchData<dim> & scratch_data,
+ CopyData & copy_data) {
+ this->cell_worker(cell, scratch_data, copy_data);
+ };
+
+ auto copier = [&](const CopyData &cd) {
+ this->constraints.distribute_local_to_global(cd.cell_matrix,
+ cd.cell_rhs,
+ cd.local_dof_indices,
+ system_matrix,
+ system_rhs);
+ };
+
+ const unsigned int n_gauss_points = degree + 1;
+
+ ScratchData<dim> scratch_data(mapping,
+ fe,
+ n_gauss_points,
+ update_values | update_gradients |
+ update_JxW_values |
+ update_quadrature_points);
+
+ MeshWorker::mesh_loop(dof_handler.begin_active(),
+ dof_handler.end(),
+ cell_worker,
+ copier,
+ scratch_data,
+ CopyData(),
+ MeshWorker::assemble_own_cells);
+ }
+
+
+ // @sect4{LaplaceProblem::assemble_multigrid}
+
+ // The next function is the one that builds the matrices
+ // that define the multigrid method on each level of the mesh. The integration
+ // core is the same as above, but the loop below will go over all existing
+ // cells instead of just the active ones, and the results must be entered into
+ // the correct level matrices. Fortunately, MeshWorker hides most of that from
+ // us, and thus the difference between this function and the previous lies
+ // only in the setup of the assembler and the different iterators in the loop.
+ //
+ // We generate an AffineConstraints<> object for each level containing the
+ // boundary and interface dofs as constrained entries. The corresponding
+ // object is then used to generate the level matrices.
+ template <int dim>
+ void LaplaceProblem<dim>::assemble_multigrid()
+ {
+ MappingQ1<dim> mapping;
+ const unsigned int n_levels = triangulation.n_levels();
+
+ std::vector<AffineConstraints<>> boundary_constraints(n_levels);
+ for (unsigned int level = 0; level < n_levels; ++level)
+ {
+ IndexSet dofset;
+ DoFTools::extract_locally_relevant_level_dofs(dof_handler,
+ level,
+ dofset);
+ boundary_constraints[level].reinit(dofset);
+ boundary_constraints[level].add_lines(
+ mg_constrained_dofs.get_refinement_edge_indices(level));
+ boundary_constraints[level].add_lines(
+ mg_constrained_dofs.get_boundary_indices(level));
+ boundary_constraints[level].close();
+ }
+
+ auto cell_worker =
+ [&](const typename DoFHandler<dim>::level_cell_iterator &cell,
+ ScratchData<dim> & scratch_data,
+ CopyData & copy_data) {
+ this->cell_worker(cell, scratch_data, copy_data);
+ };
+
+ auto copier = [&](const CopyData &cd) {
+ boundary_constraints[cd.level].distribute_local_to_global(
+ cd.cell_matrix, cd.local_dof_indices, mg_matrices[cd.level]);
+
+ const unsigned int dofs_per_cell = cd.local_dof_indices.size();
+
+ // TODO EXPLAIN:
+
+ for (unsigned int i = 0; i < dofs_per_cell; ++i)
+ for (unsigned int j = 0; j < dofs_per_cell; ++j)
+ if (mg_constrained_dofs.is_interface_matrix_entry(
+ cd.level, cd.local_dof_indices[i], cd.local_dof_indices[j]))
+ {
+ mg_interface_matrices[cd.level].add(cd.local_dof_indices[i],
+ cd.local_dof_indices[j],
+ cd.cell_matrix(i, j));
+ }
+ };
+
+ const unsigned int n_gauss_points = degree + 1;
+
+ ScratchData<dim> scratch_data(mapping,
+ fe,
+ n_gauss_points,
+ update_values | update_gradients |
+ update_JxW_values |
+ update_quadrature_points);
+
+ MeshWorker::mesh_loop(dof_handler.begin_mg(),
+ dof_handler.end_mg(),
+ cell_worker,
+ copier,
+ scratch_data,
+ CopyData(),
+ MeshWorker::assemble_own_cells);
+ }
+
+
+
+ // @sect4{LaplaceProblem::solve}
+
+ // This is the other function that is significantly different in support of
+ // the multigrid solver (or, in fact, the preconditioner for which we use
+ // the multigrid method).
+ //
+ // Let us start out by setting up two of the components of multilevel
+ // methods: transfer operators between levels, and a solver on the coarsest
+ // level. In finite element methods, the transfer operators are derived from
+ // the finite element function spaces involved and can often be computed in
+ // a generic way independent of the problem under consideration. In that
+ // case, we can use the MGTransferPrebuilt class that, given the constraints
+ // of the final linear system and the MGConstrainedDoFs object that knows
+ // about the boundary conditions on the each level and the degrees of
+ // freedom on interfaces between different refinement level can build the
+ // matrices for those transfer operations from a DoFHandler object with
+ // level degrees of freedom.
+ //
+ // The second part of the following lines deals with the coarse grid
+ // solver. Since our coarse grid is very coarse indeed, we decide for a
+ // direct solver (a Householder decomposition of the coarsest level matrix),
+ // even if its implementation is not particularly sophisticated. If our
+ // coarse mesh had many more cells than the five we have here, something
+ // better suited would obviously be necessary here.
+ template <int dim>
+ void LaplaceProblem<dim>::solve()
+ {
+ MGTransferPrebuilt<Vector<double>> mg_transfer(mg_constrained_dofs);
+ mg_transfer.build_matrices(dof_handler);
+
+ FullMatrix<double> coarse_matrix;
+ coarse_matrix.copy_from(mg_matrices[0]);
+ MGCoarseGridHouseholder<> coarse_grid_solver;
+ coarse_grid_solver.initialize(coarse_matrix);
+
+ // The next component of a multilevel solver or preconditioner is that we
+ // need a smoother on each level. A common choice for this is to use the
+ // application of a relaxation method (such as the SOR, Jacobi or Richardson
+ // method) or a small number of iterations of a solver method (such as CG or
+ // GMRES). The mg::SmootherRelaxation and MGSmootherPrecondition classes
+ // provide support for these two kinds of smoothers. Here, we opt for the
+ // application of a single SOR iteration. To this end, we define an
+ // appropriate alias and then setup a smoother object.
+ //
+ // The last step is to initialize the smoother object with our level
+ // matrices and to set some smoothing parameters. The
+ // <code>initialize()</code> function can optionally take additional
+ // arguments that will be passed to the smoother object on each level. In
+ // the current case for the SOR smoother, this could, for example, include
+ // a relaxation parameter. However, we here leave these at their default
+ // values. The call to <code>set_steps()</code> indicates that we will use
+ // two pre- and two post-smoothing steps on each level; to use a variable
+ // number of smoother steps on different levels, more options can be set
+ // in the constructor call to the <code>mg_smoother</code> object.
+ //
+ // The last step results from the fact that we use the SOR method as a
+ // smoother - which is not symmetric - but we use the conjugate gradient
+ // iteration (which requires a symmetric preconditioner) below, we need to
+ // let the multilevel preconditioner make sure that we get a symmetric
+ // operator even for nonsymmetric smoothers:
+ using Smoother = PreconditionSOR<SparseMatrix<double>>;
+ mg::SmootherRelaxation<Smoother, Vector<double>> mg_smoother;
+ mg_smoother.initialize(mg_matrices);
+ mg_smoother.set_steps(2);
+ mg_smoother.set_symmetric(true);
+
+ // The next preparatory step is that we must wrap our level and interface
+ // matrices in an object having the required multiplication functions. We
+ // will create two objects for the interface objects going from coarse to
+ // fine and the other way around; the multigrid algorithm will later use
+ // the transpose operator for the latter operation, allowing us to
+ // initialize both up and down versions of the operator with the matrices
+ // we already built:
+ mg::Matrix<Vector<double>> mg_matrix(mg_matrices);
+ mg::Matrix<Vector<double>> mg_interface_up(mg_interface_matrices);
+ mg::Matrix<Vector<double>> mg_interface_down(mg_interface_matrices);
+
+ // Now, we are ready to set up the V-cycle operator and the multilevel
+ // preconditioner.
+ Multigrid<Vector<double>> mg(
+ mg_matrix, coarse_grid_solver, mg_transfer, mg_smoother, mg_smoother);
+ mg.set_edge_matrices(mg_interface_down, mg_interface_up);
+
+ PreconditionMG<dim, Vector<double>, MGTransferPrebuilt<Vector<double>>>
+ preconditioner(dof_handler, mg, mg_transfer);
+
+ // With all this together, we can finally get about solving the linear
+ // system in the usual way:
+ SolverControl solver_control(1000, 1e-12);
+ SolverCG<> solver(solver_control);
+
+ solution = 0;
+
+ solver.solve(system_matrix, solution, system_rhs, preconditioner);
+ std::cout << " Number of CG iterations: " << solver_control.last_step()
+ << "\n"
+ << std::endl;
+ constraints.distribute(solution);
+ }
+
+
+
+ // @sect4{Postprocessing}
+
+ // The following two functions postprocess a solution once it is
+ // computed. In particular, the first one refines the mesh at the beginning
+ // of each cycle while the second one outputs results at the end of each
+ // such cycle. The functions are almost unchanged from those in step-6.
+ template <int dim>
+ void LaplaceProblem<dim>::refine_grid()
+ {
+ Vector<float> estimated_error_per_cell(triangulation.n_active_cells());
+
+ KellyErrorEstimator<dim>::estimate(
+ dof_handler,
+ QGauss<dim - 1>(degree + 2),
+ std::map<types::boundary_id, const Function<dim> *>(),
+ solution,
+ estimated_error_per_cell);
+ GridRefinement::refine_and_coarsen_fixed_number(triangulation,
+ estimated_error_per_cell,
+ 0.3,
+ 0.03);
+ triangulation.execute_coarsening_and_refinement();
+ }
+
+
+
+ template <int dim>
+ void LaplaceProblem<dim>::output_results(const unsigned int cycle) const
+ {
+ DataOut<dim> data_out;
+
+ data_out.attach_dof_handler(dof_handler);
+ data_out.add_data_vector(solution, "solution");
+ data_out.build_patches();
+
+ std::ofstream output("solution-" + std::to_string(cycle) + ".vtk");
+ data_out.write_vtk(output);
+ }
+
+
+ // @sect4{LaplaceProblem::run}
+
+ // Like several of the functions above, this is almost exactly a copy of
+ // the corresponding function in step-6. The only difference is the call to
+ // <code>assemble_multigrid</code> that takes care of forming the matrices
+ // on every level that we need in the multigrid method.
+ template <int dim>
+ void LaplaceProblem<dim>::run()
+ {
+ for (unsigned int cycle = 0; cycle < 8; ++cycle)
+ {
+ std::cout << "Cycle " << cycle << std::endl;
+
+ if (cycle == 0)
+ {
+ GridGenerator::hyper_ball(triangulation);
+ triangulation.refine_global(2);
+ }
+ else
+ refine_grid();
+
+ std::cout << " Number of active cells: "
+ << triangulation.n_active_cells() << std::endl;
+
+ setup_system();
+
+ assemble_system();
+ assemble_multigrid();
+
+ solve();
+ output_results(cycle);
+ }
+ }
+} // namespace Step16
+
+
+// @sect3{The main() function}
+//
+// This is again the same function as in step-6:
+int main()
+{
+ try
+ {
+ using namespace Step16;
+
+ LaplaceProblem<2> laplace_problem(1);
+ laplace_problem.run();
+ }
+ catch (std::exception &exc)
+ {
+ std::cerr << std::endl
+ << std::endl
+ << "----------------------------------------------------"
+ << std::endl;
+ std::cerr << "Exception on processing: " << std::endl
+ << exc.what() << std::endl
+ << "Aborting!" << std::endl
+ << "----------------------------------------------------"
+ << std::endl;
+
+ return 1;
+ }
+ catch (...)
+ {
+ std::cerr << std::endl
+ << std::endl
+ << "----------------------------------------------------"
+ << std::endl;
+ std::cerr << "Unknown exception!" << std::endl
+ << "Aborting!" << std::endl
+ << "----------------------------------------------------"
+ << std::endl;
+ return 1;
+ }
+
+ return 0;
+}
projects / dealii.git / commitdiff