Example #1
0
int main(int argc, char* argv[])
{
  // Choose a Butcher's table or define your own.
  ButcherTable bt(butcher_table_type);
  if (bt.is_explicit()) Hermes::Mixins::Loggable::Static::info("Using a %d-stage explicit R-K method.", bt.get_size());
  if (bt.is_diagonally_implicit()) Hermes::Mixins::Loggable::Static::info("Using a %d-stage diagonally implicit R-K method.", bt.get_size());
  if (bt.is_fully_implicit()) Hermes::Mixins::Loggable::Static::info("Using a %d-stage fully implicit R-K method.", bt.get_size());

  // Load the mesh.
  MeshSharedPtr mesh(new Mesh), basemesh(new Mesh);
  MeshReaderH2D mloader;
  mloader.load("square.mesh", basemesh);
  mesh->copy(basemesh);

  // Initial mesh refinements.
  for(int i = 0; i < INIT_GLOB_REF_NUM; i++) mesh->refine_all_elements();
  mesh->refine_towards_boundary("Top", INIT_REF_NUM_BDY);

  // Initialize boundary conditions.
  CustomEssentialBCNonConst bc_essential(Hermes::vector<std::string>("Bottom", "Right", "Top", "Left"));
  EssentialBCs<double> bcs(&bc_essential);

  // Create an H1 space with default shapeset.
  SpaceSharedPtr<double> space(new H1Space<double>(mesh, &bcs, P_INIT));
  int ndof_coarse = Space<double>::get_num_dofs(space);
  adaptivity.set_space(space);
  Hermes::Mixins::Loggable::Static::info("ndof_coarse = %d.", ndof_coarse);

  // Zero initial solution. This is why we use H_OFFSET.
  MeshFunctionSharedPtr<double> h_time_prev(new ZeroSolution<double>(mesh)), h_time_new(new ZeroSolution<double>(mesh));

  // Initialize the constitutive relations.
  ConstitutiveRelations* constitutive_relations;
  if(constitutive_relations_type == CONSTITUTIVE_GENUCHTEN)
    constitutive_relations = new ConstitutiveRelationsGenuchten(ALPHA, M, N, THETA_S, THETA_R, K_S, STORATIVITY);
  else
    constitutive_relations = new ConstitutiveRelationsGardner(ALPHA, THETA_S, THETA_R, K_S);

  // Initialize the weak formulation.
  CustomWeakFormRichardsRK wf(constitutive_relations);

  // Initialize the FE problem.
  DiscreteProblem<double> dp(&wf, space);

  // Create a refinement selector.
  H1ProjBasedSelector<double> selector(CAND_LIST);

  // Visualize initial condition.
  char title[100];
  ScalarView view("Initial condition", new WinGeom(0, 0, 440, 350));
  OrderView ordview("Initial mesh", new WinGeom(445, 0, 440, 350));
  view.show(h_time_prev);
  ordview.show(space);

  // DOF and CPU convergence graphs initialization.
  SimpleGraph graph_dof, graph_cpu;
  
  // Time measurement.
  Hermes::Mixins::TimeMeasurable cpu_time;
  cpu_time.tick();
  
  // Time stepping loop.
  double current_time = 0; int ts = 1;
  do 
  {
    // Periodic global derefinement.
    if (ts > 1 && ts % UNREF_FREQ == 0) 
    {
      Hermes::Mixins::Loggable::Static::info("Global mesh derefinement.");
      switch (UNREF_METHOD) {
        case 1: mesh->copy(basemesh);
                space->set_uniform_order(P_INIT);
                break;
        case 2: mesh->unrefine_all_elements();
                space->set_uniform_order(P_INIT);
                break;
        case 3: space->unrefine_all_mesh_elements();
                space->adjust_element_order(-1, -1, P_INIT, P_INIT);
                break;
        default: throw Hermes::Exceptions::Exception("Wrong global derefinement method.");
      }

      space->assign_dofs();
      ndof_coarse = Space<double>::get_num_dofs(space);
    }

    // Spatial adaptivity loop. Note: h_time_prev must not be changed 
    // during spatial adaptivity. 
    bool done = false; int as = 1;
    double err_est;
    do {
      Hermes::Mixins::Loggable::Static::info("Time step %d, adaptivity step %d:", ts, as);

      // Construct globally refined reference mesh and setup reference space.
      Mesh::ReferenceMeshCreator refMeshCreator(mesh);
      MeshSharedPtr ref_mesh = refMeshCreator.create_ref_mesh();

      Space<double>::ReferenceSpaceCreator refSpaceCreator(space, ref_mesh);
      SpaceSharedPtr<double> ref_space = refSpaceCreator.create_ref_space();
      int ndof_ref = Space<double>::get_num_dofs(ref_space);

      // Time measurement.
      cpu_time.tick();

      // Initialize Runge-Kutta time stepping.
      RungeKutta<double> runge_kutta(&wf, ref_space, &bt);

      // Perform one Runge-Kutta time step according to the selected Butcher's table.
      Hermes::Mixins::Loggable::Static::info("Runge-Kutta time step (t = %g s, tau = %g s, stages: %d).",
           current_time, time_step, bt.get_size());
      try
      {
        runge_kutta.set_time(current_time);
        runge_kutta.set_time_step(time_step);
        runge_kutta.set_max_allowed_iterations(NEWTON_MAX_ITER);
        runge_kutta.set_tolerance(NEWTON_TOL);
        runge_kutta.rk_time_step_newton(h_time_prev, h_time_new);
      }
      catch(Exceptions::Exception& e)
      {
        e.print_msg();
        throw Hermes::Exceptions::Exception("Runge-Kutta time step failed");
      }

      // Project the fine mesh solution onto the coarse mesh.
      MeshFunctionSharedPtr<double> sln_coarse(new Solution<double>);
      Hermes::Mixins::Loggable::Static::info("Projecting fine mesh solution on coarse mesh for error estimation.");
      OGProjection<double> ogProjection; ogProjection.project_global(space, h_time_new, sln_coarse); 

      // Calculate element errors and total error estimate.
      Hermes::Mixins::Loggable::Static::info("Calculating error estimate.");
      errorCalculator.calculate_errors(sln_coarse, h_time_new, true);
      double err_est_rel_total = errorCalculator.get_total_error_squared() * 100;

      // Report results.
      Hermes::Mixins::Loggable::Static::info("ndof_coarse: %d, ndof_ref: %d, err_est_rel: %g%%", 
           Space<double>::get_num_dofs(space), Space<double>::get_num_dofs(ref_space), err_est_rel_total);

      // Time measurement.
      cpu_time.tick();

      // If err_est too large, adapt the mesh.
      if (err_est_rel_total < ERR_STOP) done = true;
      else 
      {
        Hermes::Mixins::Loggable::Static::info("Adapting the coarse mesh.");
        done = adaptivity.adapt(&selector);

        // Increase the counter of performed adaptivity steps.
        as++;
      }
    }
    while (done == false);

    // Add entry to DOF and CPU convergence graphs.
    graph_dof.add_values(current_time, Space<double>::get_num_dofs(space));
    graph_dof.save("conv_dof_est.dat");
    graph_cpu.add_values(current_time, cpu_time.accumulated());
    graph_cpu.save("conv_cpu_est.dat");

    // Visualize the solution and mesh->
    char title[100];
    sprintf(title, "Solution, time %g", current_time);
    view.set_title(title);
    view.show_mesh(false);
    view.show(h_time_new);
    sprintf(title, "Mesh, time %g", current_time);
    ordview.set_title(title);
    ordview.show(space);

    // Copy last reference solution into h_time_prev.
    h_time_prev->copy(h_time_new);

    // Increase current time and counter of time steps.
    current_time += time_step;
    ts++;
  }
  while (current_time < T_FINAL);

  // Wait for all views to be closed.
  View::wait();
  return 0;
}
Example #2
0
int main(int argc, char* argv[])
{
  // Load the mesh.
  MeshSharedPtr mesh(new Mesh);
  MeshReaderH2D mloader;
  mloader.load("square.mesh", mesh);

  // Initial mesh refinements.
  for (int i = 0; i < INIT_GLOB_REF_NUM; i++) mesh->refine_all_elements();
  mesh->refine_towards_boundary("Top", INIT_REF_NUM_BDY);

  // Initialize boundary conditions.
  CustomEssentialBCNonConst bc_essential({ "Bottom", "Right", "Top", "Left" });
  EssentialBCs<double> bcs(&bc_essential);

  // Create an H1 space with default shapeset.
  SpaceSharedPtr<double> space(new H1Space<double>(mesh, &bcs, P_INIT));
  int ndof = space->get_num_dofs();
  Hermes::Mixins::Loggable::Static::info("ndof = %d.", ndof);

  // Zero initial solutions. This is why we use H_OFFSET.
  MeshFunctionSharedPtr<double> h_time_prev(new ZeroSolution<double>(mesh));

  // Initialize views.
  ScalarView view("Initial condition", new WinGeom(0, 0, 600, 500));
  view.fix_scale_width(80);

  // Visualize the initial condition.
  view.show(h_time_prev);

  // Initialize the constitutive relations.
  ConstitutiveRelations* constitutive_relations;
  if (constitutive_relations_type == CONSTITUTIVE_GENUCHTEN)
    constitutive_relations = new ConstitutiveRelationsGenuchten(ALPHA, M, N, THETA_S, THETA_R, K_S, STORATIVITY);
  else
    constitutive_relations = new ConstitutiveRelationsGardner(ALPHA, THETA_S, THETA_R, K_S);

  // Initialize the weak formulation.
  double current_time = 0;
  WeakFormSharedPtr<double> wf(new CustomWeakFormRichardsIE(time_step, h_time_prev, constitutive_relations));

  // Initialize the FE problem.
  DiscreteProblem<double> dp(wf, space);

  // Initialize Newton solver.
  NewtonSolver<double> newton(&dp);
  newton.set_verbose_output(true);

  // Time stepping:
  int ts = 1;
  do
  {
    Hermes::Mixins::Loggable::Static::info("---- Time step %d, time %3.5f s", ts, current_time);

    // Perform Newton's iteration.
    try
    {
      newton.set_max_allowed_iterations(NEWTON_MAX_ITER);
      newton.solve();
    }
    catch (Hermes::Exceptions::Exception e)
    {
      e.print_msg();
      throw Hermes::Exceptions::Exception("Newton's iteration failed.");
    };

    // Translate the resulting coefficient vector into the Solution<double> sln->
    Solution<double>::vector_to_solution(newton.get_sln_vector(), space, h_time_prev);

    // Visualize the solution.
    char title[100];
    sprintf(title, "Time %g s", current_time);
    view.set_title(title);
    view.show(h_time_prev);

    // Increase current time and time step counter.
    current_time += time_step;
    ts++;
  } while (current_time < T_FINAL);

  // Wait for the view to be closed.
  View::wait();
  return 0;
}
Example #3
0
int main(int argc, char* argv[])
{
  // Load the mesh.
  Mesh mesh;
  MeshReaderH2D mloader;
  mloader.load("square.mesh", &mesh);

  // Initial mesh refinements.
  for(int i = 0; i < INIT_GLOB_REF_NUM; i++) mesh.refine_all_elements();
  mesh.refine_towards_boundary("Top", INIT_REF_NUM_BDY);

  // Initialize boundary conditions.
  CustomEssentialBCNonConst bc_essential(Hermes::vector<std::string>("Bottom", 
      "Right", "Top", "Left"));
  EssentialBCs<double> bcs(&bc_essential);

  // Create an H1 space with default shapeset.
  H1Space<double> space(&mesh, &bcs, P_INIT);
  int ndof = space.get_num_dofs();
  info("ndof = %d.", ndof);

  // Zero initial solutions. This is why we use H_OFFSET.
  ZeroSolution h_time_prev(&mesh), h_iter_prev(&mesh);

  // Initialize views.
  ScalarView view("Initial condition", new WinGeom(0, 0, 600, 500));
  view.fix_scale_width(80);

  // Visualize the initial condition.
  view.show(&h_time_prev);

  // Initialize the constitutive relations.
  ConstitutiveRelations* constitutive_relations;
  if(constitutive_relations_type == CONSTITUTIVE_GENUCHTEN)
    constitutive_relations = new ConstitutiveRelationsGenuchten(ALPHA, M, N, THETA_S, THETA_R, K_S, STORATIVITY);
  else
    constitutive_relations = new ConstitutiveRelationsGardner(ALPHA, THETA_S, THETA_R, K_S);

  // Initialize the weak formulation.
  double current_time = 0;
  CustomWeakFormRichardsIEPicard wf(time_step, &h_time_prev, &h_iter_prev, constitutive_relations);

  // Initialize the FE problem.
  DiscreteProblem<double> dp(&wf, &space);

  // Initialize the Picard solver.
  PicardSolver<double> picard(&dp, &h_iter_prev, matrix_solver);
  picard.set_verbose_output(true);

  // Time stepping:
  int ts = 1;
  do 
  {
    info("---- Time step %d, time %3.5f s", ts, current_time);

    // Perform the Picard's iteration (Anderson acceleration on by default).
    if (!picard.solve(PICARD_TOL, PICARD_MAX_ITER, PICARD_NUM_LAST_ITER_USED, 
        PICARD_ANDERSON_BETA)) error("Picard's iteration failed.");

    // Translate the coefficient vector into a Solution. 
    Solution<double>::vector_to_solution(picard.get_sln_vector(), &space, &h_iter_prev);

    // Increase current time and time step counter.
    current_time += time_step;
    ts++;

    // Visualize the solution.
    char title[100];
    sprintf(title, "Time %g s", current_time);
    view.set_title(title);
    view.show(&h_iter_prev);

    // Save the next time level solution.
    h_time_prev.copy(&h_iter_prev);
  }
  while (current_time < T_FINAL);

  // Wait for the view to be closed.
  View::wait();
  return 0;
}
Example #4
0
int main(int argc, char* argv[])
{
  // Choose a Butcher's table or define your own.
  ButcherTable bt(butcher_table_type);
  if (bt.is_explicit()) info("Using a %d-stage explicit R-K method.", bt.get_size());
  if (bt.is_diagonally_implicit()) info("Using a %d-stage diagonally implicit R-K method.", bt.get_size());
  if (bt.is_fully_implicit()) info("Using a %d-stage fully implicit R-K method.", bt.get_size());

  // Load the mesh.
  Mesh mesh, basemesh;
  MeshReaderH2D mloader;
  mloader.load("square.mesh", &basemesh);
  mesh.copy(&basemesh);

  // Initial mesh refinements.
  for(int i = 0; i < INIT_GLOB_REF_NUM; i++) mesh.refine_all_elements();
  mesh.refine_towards_boundary("Top", INIT_REF_NUM_BDY);

  // Initialize boundary conditions.
  CustomEssentialBCNonConst bc_essential(Hermes::vector<std::string>("Bottom", "Right", "Top", "Left"));
  EssentialBCs<double> bcs(&bc_essential);

  // Create an H1 space with default shapeset.
  H1Space<double> space(&mesh, &bcs, P_INIT);
  int ndof_coarse = Space<double>::get_num_dofs(&space);
  info("ndof_coarse = %d.", ndof_coarse);

  // Zero initial solution. This is why we use H_OFFSET.
  ZeroSolution h_time_prev(&mesh), h_time_new(&mesh);

  // Initialize the constitutive relations.
  ConstitutiveRelations* constitutive_relations;
  if(constitutive_relations_type == CONSTITUTIVE_GENUCHTEN)
    constitutive_relations = new ConstitutiveRelationsGenuchten(ALPHA, M, N, THETA_S, THETA_R, K_S, STORATIVITY);
  else
    constitutive_relations = new ConstitutiveRelationsGardner(ALPHA, THETA_S, THETA_R, K_S);

  // Initialize the weak formulation.
  CustomWeakFormRichardsRK wf(constitutive_relations);

  // Initialize the FE problem.
  DiscreteProblem<double> dp(&wf, &space);

  // Create a refinement selector.
  H1ProjBasedSelector<double> selector(CAND_LIST, CONV_EXP, H2DRS_DEFAULT_ORDER);

  // Visualize initial condition.
  char title[100];
  ScalarView view("Initial condition", new WinGeom(0, 0, 440, 350));
  OrderView ordview("Initial mesh", new WinGeom(445, 0, 440, 350));
  view.show(&h_time_prev);
  ordview.show(&space);

  // DOF and CPU convergence graphs initialization.
  SimpleGraph graph_dof, graph_cpu;
  
  // Time measurement.
  TimePeriod cpu_time;
  cpu_time.tick();
  
  // Time stepping loop.
  double current_time = 0; int ts = 1;
  do 
  {
    // Periodic global derefinement.
    if (ts > 1 && ts % UNREF_FREQ == 0) 
    {
      info("Global mesh derefinement.");
      switch (UNREF_METHOD) {
        case 1: mesh.copy(&basemesh);
                space.set_uniform_order(P_INIT);
                break;
        case 2: mesh.unrefine_all_elements();
                space.set_uniform_order(P_INIT);
                break;
        case 3: space.unrefine_all_mesh_elements();
                space.adjust_element_order(-1, -1, P_INIT, P_INIT);
                break;
        default: error("Wrong global derefinement method.");
      }

      ndof_coarse = Space<double>::get_num_dofs(&space);
    }

    // Spatial adaptivity loop. Note: h_time_prev must not be changed 
    // during spatial adaptivity. 
    bool done = false; int as = 1;
    double err_est;
    do {
      info("Time step %d, adaptivity step %d:", ts, as);

      // Construct globally refined reference mesh and setup reference space.
      Space<double>* ref_space = Space<double>::construct_refined_space(&space);
      int ndof_ref = Space<double>::get_num_dofs(ref_space);

      // Time measurement.
      cpu_time.tick();

      // Initialize Runge-Kutta time stepping.
      RungeKutta<double> runge_kutta(&wf, ref_space, &bt, matrix_solver);

      // Perform one Runge-Kutta time step according to the selected Butcher's table.
      info("Runge-Kutta time step (t = %g s, tau = %g s, stages: %d).",
           current_time, time_step, bt.get_size());
      bool freeze_jacobian = false;
      bool block_diagonal_jacobian = false;
      bool verbose = true;
      double damping_coeff = 1.0;
      double max_allowed_residual_norm = 1e10;

      try
      {
        runge_kutta.rk_time_step_newton(current_time, time_step, &h_time_prev, 
            &h_time_new, freeze_jacobian, block_diagonal_jacobian, verbose,
            NEWTON_TOL, NEWTON_MAX_ITER, damping_coeff, max_allowed_residual_norm);
      }
      catch(Exceptions::Exception& e)
      {
        e.printMsg();
        error("Runge-Kutta time step failed");
      }

      // Project the fine mesh solution onto the coarse mesh.
      Solution<double> sln_coarse;
      info("Projecting fine mesh solution on coarse mesh for error estimation.");
      OGProjection<double>::project_global(&space, &h_time_new, &sln_coarse, matrix_solver); 

      // Calculate element errors and total error estimate.
      info("Calculating error estimate.");
      Adapt<double>* adaptivity = new Adapt<double>(&space);
      double err_est_rel_total = adaptivity->calc_err_est(&sln_coarse, &h_time_new) * 100;

      // Report results.
      info("ndof_coarse: %d, ndof_ref: %d, err_est_rel: %g%%", 
           Space<double>::get_num_dofs(&space), Space<double>::get_num_dofs(ref_space), err_est_rel_total);

      // Time measurement.
      cpu_time.tick();

      // If err_est too large, adapt the mesh.
      if (err_est_rel_total < ERR_STOP) done = true;
      else 
      {
        info("Adapting the coarse mesh.");
        done = adaptivity->adapt(&selector, THRESHOLD, STRATEGY, MESH_REGULARITY);

        if (Space<double>::get_num_dofs(&space) >= NDOF_STOP) 
          done = true;
        else
          // Increase the counter of performed adaptivity steps.
          as++;
      }
      
      // Clean up.
      delete adaptivity;
      if(!done)
      {
        delete h_time_new.get_space();
        delete h_time_new.get_mesh();
      }
    }
    while (done == false);

    // Add entry to DOF and CPU convergence graphs.
    graph_dof.add_values(current_time, Space<double>::get_num_dofs(&space));
    graph_dof.save("conv_dof_est.dat");
    graph_cpu.add_values(current_time, cpu_time.accumulated());
    graph_cpu.save("conv_cpu_est.dat");

    // Visualize the solution and mesh.
    char title[100];
    sprintf(title, "Solution, time %g", current_time);
    view.set_title(title);
    view.show_mesh(false);
    view.show(&h_time_new);
    sprintf(title, "Mesh, time %g", current_time);
    ordview.set_title(title);
    ordview.show(&space);

    // Copy last reference solution into h_time_prev.
    h_time_prev.copy(&h_time_new);
    delete h_time_new.get_mesh();

    // Increase current time and counter of time steps.
    current_time += time_step;
    ts++;
  }
  while (current_time < T_FINAL);

  // Wait for all views to be closed.
  View::wait();
  return 0;
}
Example #5
0
// Main function.
int main(int argc, char* argv[])
{
  ConstitutiveRelationsGenuchtenWithLayer constitutive_relations(CONSTITUTIVE_TABLE_METHOD, NUM_OF_INSIDE_PTS, LOW_LIMIT, TABLE_PRECISION, TABLE_LIMIT, K_S_vals, ALPHA_vals, N_vals, M_vals, THETA_R_vals, THETA_S_vals, STORATIVITY_vals);

  // Either use exact constitutive relations (slow) (method 0) or precalculate 
  // their linear approximations (faster) (method 1) or
  // precalculate their quintic polynomial approximations (method 2) -- managed by 
  // the following loop "Initializing polynomial approximation".
  if (CONSTITUTIVE_TABLE_METHOD == 1)
    constitutive_relations.constitutive_tables_ready = get_constitutive_tables(1, &constitutive_relations, MATERIAL_COUNT);  // 1 stands for the Newton's method.
  

  // The van Genuchten + Mualem K(h) function is approximated by polynomials close 
  // to zero in case of CONSTITUTIVE_TABLE_METHOD==1.
  // In case of CONSTITUTIVE_TABLE_METHOD==2, all constitutive functions are approximated by polynomials.
  info("Initializing polynomial approximations.");
  for (int i=0; i < MATERIAL_COUNT; i++)
  {
    // Points to be used for polynomial approximation of K(h).
    double* points = new double[NUM_OF_INSIDE_PTS];

    init_polynomials(6 + NUM_OF_INSIDE_PTS, LOW_LIMIT, points, NUM_OF_INSIDE_PTS, i, &constitutive_relations, MATERIAL_COUNT, NUM_OF_INTERVALS, INTERVALS_4_APPROX);
  }
  
  constitutive_relations.polynomials_ready = true;
  if (CONSTITUTIVE_TABLE_METHOD == 2)
  {
    constitutive_relations.constitutive_tables_ready = true;
    //Assign table limit to global definition.
    constitutive_relations.table_limit = INTERVALS_4_APPROX[NUM_OF_INTERVALS-1];
  }
  
  // Choose a Butcher's table or define your own.
  ButcherTable bt(butcher_table_type);
  if (bt.is_explicit()) info("Using a %d-stage explicit R-K method.", bt.get_size());
  if (bt.is_diagonally_implicit()) info("Using a %d-stage diagonally implicit R-K method.", bt.get_size());
  if (bt.is_fully_implicit()) info("Using a %d-stage fully implicit R-K method.", bt.get_size());

  // Load the mesh.
  Mesh mesh, basemesh;
  MeshReaderH2D mloader;
  mloader.load(mesh_file, &basemesh);
  
  // Perform initial mesh refinements.
  mesh.copy(&basemesh);
  for(int i = 0; i < INIT_REF_NUM; i++) mesh.refine_all_elements();
  mesh.refine_towards_boundary("Top", INIT_REF_NUM_BDY_TOP);

  // Initialize boundary conditions.
  RichardsEssentialBC bc_essential("Top", H_ELEVATION, PULSE_END_TIME, H_INIT, STARTUP_TIME);
  EssentialBCs<double> bcs(&bc_essential);

  // Create an H1 space with default shapeset.
  H1Space<double> space(&mesh, &bcs, P_INIT);
  int ndof = space.get_num_dofs();
  info("ndof = %d.", ndof);

  // Convert initial condition into a Solution.
  ZeroSolution h_time_prev(&mesh), h_time_new(&mesh), time_error_fn(&mesh);

  // Initialize views.
  ScalarView view("Initial condition", new WinGeom(0, 0, 600, 500));
  view.fix_scale_width(80);

  // Visualize the initial condition.
  view.show(&h_time_prev);

  // Initialize the weak formulation.
  CustomWeakFormRichardsRK wf(&constitutive_relations);

   // Visualize the projection and mesh.
  ScalarView sview("Initial condition", new WinGeom(0, 0, 400, 350));
  sview.fix_scale_width(50);
  sview.show(&h_time_prev, HERMES_EPS_VERYHIGH);
  ScalarView eview("Temporal error", new WinGeom(405, 0, 400, 350));
  eview.fix_scale_width(50);
  eview.show(&time_error_fn, HERMES_EPS_VERYHIGH);
  OrderView oview("Initial mesh", new WinGeom(810, 0, 350, 350));
  oview.show(&space);

  // Graph for time step history.
  SimpleGraph time_step_graph;
  info("Time step history will be saved to file time_step_history.dat.");

  // Initialize Runge-Kutta time stepping.
  RungeKutta<double> runge_kutta(&wf, &space, &bt, matrix_solver);

  // Time stepping:
  double current_time = 0;
  int ts = 1;
  do 
  {
    info("---- Time step %d, time %3.5f s", ts, current_time);

    Space<double>::update_essential_bc_values(&space, current_time);

    // Perform one Runge-Kutta time step according to the selected Butcher's table.
    info("Runge-Kutta time step (t = %g s, time step = %g s, stages: %d).", 
         current_time, time_step, bt.get_size());
    bool freeze_jacobian = false;
    bool block_diagonal_jacobian = false;
    bool verbose = true;
    double damping_coeff = 1.0;
    double max_allowed_residual_norm = 1e10;

    try
    {
      runge_kutta.rk_time_step_newton(current_time, time_step, &h_time_prev, 
          &h_time_new, &time_error_fn, freeze_jacobian, block_diagonal_jacobian, verbose,
          NEWTON_TOL, NEWTON_MAX_ITER, damping_coeff, max_allowed_residual_norm);
    }
    catch(Exceptions::Exception& e)
    {
      info("Runge-Kutta time step failed, decreasing time step size from %g to %g days.", 
           time_step, time_step * time_step_dec);
      time_step *= time_step_dec;
      if (time_step < time_step_min) 
        error("Time step became too small.");
      continue;
    }
    
    // Copy solution for the new time step.
    h_time_prev.copy(&h_time_new);

    // Show error function.
    char title[100];
    sprintf(title, "Temporal error, t = %g", current_time);
    eview.set_title(title);
    eview.show(&time_error_fn, HERMES_EPS_VERYHIGH);

    // Calculate relative time stepping error and decide whether the 
    // time step can be accepted. If not, then the time step size is 
    // reduced and the entire time step repeated. If yes, then another
    // check is run, and if the relative error is very low, time step 
    // is increased.
    double rel_err_time = Global<double>::calc_norm(&time_error_fn, HERMES_H1_NORM) / Global<double>::calc_norm(&h_time_new, HERMES_H1_NORM) * 100;
    info("rel_err_time = %g%%", rel_err_time);
    if (rel_err_time > time_tol_upper) {
      info("rel_err_time above upper limit %g%% -> decreasing time step from %g to %g days and repeating time step.", 
           time_tol_upper, time_step, time_step * time_step_dec);
      time_step *= time_step_dec;
      continue;
    }
    if (rel_err_time < time_tol_lower) {
      info("rel_err_time = below lower limit %g%% -> increasing time step from %g to %g days", 
           time_tol_lower, time_step, time_step * time_step_inc);
      time_step *= time_step_inc;
    }

    // Add entry to the timestep graph.
    time_step_graph.add_values(current_time, time_step);
    time_step_graph.save("time_step_history.dat");

    // Update time.
    current_time += time_step;

    // Show the new time level solution.
    sprintf(title, "Solution, t = %g", current_time);
    sview.set_title(title);
    sview.show(&h_time_new, HERMES_EPS_VERYHIGH);
    oview.show(&space);

    // Save complete Solution.
    char filename[100];
    sprintf(filename, "outputs/tsln_%f.dat", current_time);
    h_time_new.save(filename);
    info("Solution at time %g saved to file %s.", current_time, filename);

    // Save solution for the next time step.
    h_time_prev.copy(&h_time_new);

    // Increase time step counter.
    ts++;
  } 
  while (current_time < T_FINAL);

  // Wait for the view to be closed.
  View::wait();
  return 0;
}