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Add different variants of p-multgrid #1209

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Jul 31, 2024
Merged

Add different variants of p-multgrid #1209

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74db88f
Add p-multgrid
peterrum Jul 27, 2024
5fcd72b
Add p-mg and hybrid strategies to doc
lpsaavedra Jul 31, 2024
6b57599
Correct minor typo in doc
lpsaavedra Jul 31, 2024
a1c0e8a
Add changelog entry
lpsaavedra Jul 31, 2024
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16 changes: 16 additions & 0 deletions include/core/parameters.h
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Original file line number Diff line number Diff line change
Expand Up @@ -38,6 +38,8 @@
#include <deal.II/base/parameter_handler.h>
#include <deal.II/base/parsed_function.h>

#include <deal.II/multigrid/mg_transfer_global_coarsening.h>


using namespace dealii;

Expand Down Expand Up @@ -1187,6 +1189,20 @@ namespace Parameters
/// MG enable hessians in jacobian
bool mg_enable_hessians_jacobian;

/// Type of multigrid
enum class MultigridCoarseningSequenceType
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{
h,
p,
hp,
ph
};
MultigridCoarseningSequenceType mg_coarsening_type;

/// Type of p coarsening sequence
MGTransferGlobalCoarseningTools::PolynomialCoarseningSequenceType
mg_p_coarsening_type;

/// MG smoother number of iterations
int mg_smoother_iterations;

Expand Down
47 changes: 47 additions & 0 deletions source/core/parameters.cc
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Expand Up @@ -2550,6 +2550,17 @@ namespace Parameters
Patterns::Bool(),
"use elements with linear interpolation for coarse grid");

prm.declare_entry("mg coarsening type",
"h",
Patterns::Selection("h|p|hp|ph"),
"mg coarsening type for gcmg");

prm.declare_entry("mg p coarsening type",
"decrease by one",
Patterns::Selection(
"decrease by one|bisect|go to one"),
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What is bisect?

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From the deal.II documentation:

Screenshot from 2024-07-30 19-47-19

"mg p coarsening type for gcmg");

prm.declare_entry("mg gmres max iterations",
"2000",
Patterns::Integer(),
Expand Down Expand Up @@ -2706,6 +2717,42 @@ namespace Parameters

mg_use_fe_q_iso_q1 = prm.get_bool("mg coarse grid use fe q iso q1");

const std::string mg_coarsening_type = prm.get("mg coarsening type");
if (mg_coarsening_type == "h")
this->mg_coarsening_type = MultigridCoarseningSequenceType::h;
else if (mg_coarsening_type == "p")
this->mg_coarsening_type = MultigridCoarseningSequenceType::p;
else if (mg_coarsening_type == "hp")
this->mg_coarsening_type = MultigridCoarseningSequenceType::hp;
else if (mg_coarsening_type == "ph")
this->mg_coarsening_type = MultigridCoarseningSequenceType::ph;
else
AssertThrow(false, ExcNotImplemented());

const std::string mg_p_coarsening_type =
prm.get("mg p coarsening type");
if (mg_p_coarsening_type == "decrease by one")
this->mg_p_coarsening_type = MGTransferGlobalCoarseningTools::
PolynomialCoarseningSequenceType::decrease_by_one;
else if (mg_p_coarsening_type == "bisect")
this->mg_p_coarsening_type = MGTransferGlobalCoarseningTools::
PolynomialCoarseningSequenceType::bisect;
else if (mg_p_coarsening_type == "go to one")
this->mg_p_coarsening_type = MGTransferGlobalCoarseningTools::
PolynomialCoarseningSequenceType::go_to_one;
else
AssertThrow(false, ExcNotImplemented());

AssertThrow((!mg_use_fe_q_iso_q1) ||
(this->mg_coarsening_type ==
MultigridCoarseningSequenceType::h),
ExcNotImplemented());

AssertThrow((preconditioner != PreconditionerType::lsmg) ||
(this->mg_coarsening_type ==
MultigridCoarseningSequenceType::h),
ExcNotImplemented());

mg_gmres_max_iterations = prm.get_integer("mg gmres max iterations");
mg_gmres_tolerance = prm.get_double("mg gmres tolerance");
mg_gmres_reduce = prm.get_double("mg gmres reduce");
Expand Down
88 changes: 81 additions & 7 deletions source/solvers/mf_navier_stokes.cc
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Expand Up @@ -535,6 +535,10 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(
.preconditioner ==
Parameters::LinearSolver::PreconditionerType::gcmg)
{
AssertThrow(*cell_quadrature ==
QGauss<dim>(this->dof_handler.get_fe().degree + 1),
ExcNotImplemented());

// Create triangulations
this->mg_setup_timer.enter_subsection("Create level triangulations");
this->coarse_grid_triangulations =
Expand Down Expand Up @@ -599,10 +603,68 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(

this->coarse_grid_triangulations = temp;

// p-multigrid
const auto mg_coarsening_type =
this->simulation_parameters.linear_solver.at(PhysicsID::fluid_dynamics)
.mg_coarsening_type;

const auto polynomial_coarsening_sequence =
MGTransferGlobalCoarseningTools::create_polynomial_coarsening_sequence(
this->dof_handler.get_fe().degree,
this->simulation_parameters.linear_solver
.at(PhysicsID::fluid_dynamics)
.mg_p_coarsening_type);

std::vector<std::pair<unsigned int, unsigned int>> levels;

if (mg_coarsening_type ==
Parameters::LinearSolver::MultigridCoarseningSequenceType::hp)
{
// p
for (const auto i : polynomial_coarsening_sequence)
levels.emplace_back(0, i);

// h
for (unsigned int i = 1; i < this->coarse_grid_triangulations.size();
++i)
levels.emplace_back(i, polynomial_coarsening_sequence.back());
}
else if (mg_coarsening_type ==
Parameters::LinearSolver::MultigridCoarseningSequenceType::ph)
{
// h
for (unsigned int i = 0;
i < this->coarse_grid_triangulations.size() - 1;
++i)
levels.emplace_back(i, polynomial_coarsening_sequence.front());

// p
for (const auto i : polynomial_coarsening_sequence)
levels.emplace_back(this->coarse_grid_triangulations.size() - 1, i);
}
else if (mg_coarsening_type ==
Parameters::LinearSolver::MultigridCoarseningSequenceType::p)
{
// p
for (const auto i : polynomial_coarsening_sequence)
levels.emplace_back(this->coarse_grid_triangulations.size() - 1, i);
}
else if (mg_coarsening_type ==
Parameters::LinearSolver::MultigridCoarseningSequenceType::h)
{
// h
for (unsigned int i = 0; i < this->coarse_grid_triangulations.size();
++i)
levels.emplace_back(i, polynomial_coarsening_sequence.back());
}
else
{
AssertThrow(false, ExcNotImplemented());
}

// Define maximum and minimum level according to triangulations
const unsigned int n_h_levels = this->coarse_grid_triangulations.size();
this->minlevel = 0;
this->maxlevel = n_h_levels - 1;
this->minlevel = 0;
this->maxlevel = levels.size() - 1;

// Local object for constraints of the different levels
MGLevelObject<AffineConstraints<typename VectorType::value_type>>
Expand All @@ -620,7 +682,8 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(

for (unsigned int l = this->minlevel; l <= this->maxlevel; ++l)
{
this->dof_handlers[l].reinit(*this->coarse_grid_triangulations[l]);
this->dof_handlers[l].reinit(
*this->coarse_grid_triangulations[levels[l].first]);

// To use elements with linear interpolation for coarse-grid we need
// to create the min level dof handler with the appropriate element
Expand All @@ -630,6 +693,11 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(
.mg_use_fe_q_iso_q1 &&
l == this->minlevel)
{
AssertThrow(
mg_coarsening_type ==
Parameters::LinearSolver::MultigridCoarseningSequenceType::h,
ExcNotImplemented());

const auto points =
QGaussLobatto<1>(this->dof_handler.get_fe().degree + 1)
.get_points();
Expand All @@ -638,7 +706,8 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(
FESystem<dim>(FE_Q_iso_Q1<dim>(points), dim + 1));
}
else
this->dof_handlers[l].distribute_dofs(this->dof_handler.get_fe());
this->dof_handlers[l].distribute_dofs(
FESystem<dim>(FE_Q<dim>(levels[l].second), dim + 1));
}

this->mg_setup_timer.leave_subsection(
Expand All @@ -654,7 +723,7 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(
++level)
this->pcout << " Level " << level << ": "
<< this->dof_handlers[level].n_dofs() << " DoFs, "
<< this->coarse_grid_triangulations[level]
<< this->coarse_grid_triangulations[levels[level].first]
->n_global_active_cells()
<< " cells" << std::endl;
this->pcout << std::endl;
Expand Down Expand Up @@ -802,12 +871,17 @@ MFNavierStokesPreconditionGMG<dim>::MFNavierStokesPreconditionGMG(

// Provide appropriate quadrature depending on the type of elements of
// the level
auto quadrature_mg = *cell_quadrature;
Quadrature<dim> quadrature_mg = QGauss<dim>(levels[level].second + 1);
if (this->simulation_parameters.linear_solver
.at(PhysicsID::fluid_dynamics)
.mg_use_fe_q_iso_q1 &&
level == this->minlevel)
{
AssertThrow(
mg_coarsening_type ==
Parameters::LinearSolver::MultigridCoarseningSequenceType::h,
ExcNotImplemented());

const auto points =
QGaussLobatto<1>(this->dof_handler.get_fe().degree + 1)
.get_points();
Expand Down
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