Reference documentation for deal.II version 9.2.0

#include <deal.II/lac/trilinos_precondition.h>

## Public Member Functions

AdditionalData (const bool elliptic=true, const bool higher_order_elements=false, const unsigned int n_cycles=1, const bool w_cyle=false, const double aggregation_threshold=1e-4, const std::vector< std::vector< bool >> &constant_modes=std::vector< std::vector< bool >>(0), const unsigned int smoother_sweeps=2, const unsigned int smoother_overlap=0, const bool output_details=false, const char *smoother_type="Chebyshev", const char *coarse_type="Amesos-KLU")

void set_parameters (Teuchos::ParameterList &parameter_list, std::unique_ptr< Epetra_MultiVector > &distributed_constant_modes, const Epetra_RowMatrix &matrix) const

void set_parameters (Teuchos::ParameterList &parameter_list, std::unique_ptr< Epetra_MultiVector > &distributed_constant_modes, const SparseMatrix &matrix) const

void set_operator_null_space (Teuchos::ParameterList &parameter_list, std::unique_ptr< Epetra_MultiVector > &distributed_constant_modes, const Epetra_RowMatrix &matrix) const

void set_operator_null_space (Teuchos::ParameterList &parameter_list, std::unique_ptr< Epetra_MultiVector > &distributed_constant_modes, const SparseMatrix &matrix) const

## Public Attributes

bool elliptic

bool higher_order_elements

unsigned int n_cycles

bool w_cycle

double aggregation_threshold

std::vector< std::vector< bool > > constant_modes

unsigned int smoother_sweeps

unsigned int smoother_overlap

bool output_details

const char * smoother_type

const char * coarse_type

## Detailed Description

A data structure that is used to control details of how the algebraic multigrid is set up. The flags detailed in here are then passed to the Trilinos ML implementation. A structure of the current type are passed to the constructor of PreconditionAMG.

Definition at line 1370 of file trilinos_precondition.h.

## Constructor & Destructor Documentation

 TrilinosWrappers::PreconditionAMG::AdditionalData::AdditionalData ( const bool elliptic = true, const bool higher_order_elements = false, const unsigned int n_cycles = 1, const bool w_cyle = false, const double aggregation_threshold = 1e-4, const std::vector< std::vector< bool >> & constant_modes = std::vector>(0), const unsigned int smoother_sweeps = 2, const unsigned int smoother_overlap = 0, const bool output_details = false, const char * smoother_type = "Chebyshev", const char * coarse_type = "Amesos-KLU" )

Constructor. By default, we pretend to work on elliptic problems with linear finite elements on a scalar equation.

Making use of the DoFTools::extract_constant_modes() function, the constant_modes vector can be initialized for a given field in the following manner:

...
DoFHandlerType<...> dof_handler;
FEValuesExtractors::Type... field_extractor;
...
dof_handler,
data.constant_modes );

Definition at line 39 of file trilinos_precondition_ml.cc.

## ◆ set_parameters() [1/2]

 void TrilinosWrappers::PreconditionAMG::AdditionalData::set_parameters ( Teuchos::ParameterList & parameter_list, std::unique_ptr< Epetra_MultiVector > & distributed_constant_modes, const Epetra_RowMatrix & matrix ) const

Fill in a parameter_list that can be used to initialize the AMG preconditioner.

The matrix is used in conjunction with the constant_modes to configure the null space settings for the preconditioner. The distributed_constant_modes are initialized by this function, and must remain in scope until PreconditionAMG::initialize() has been called.

Note
The set parameters reflect the current settings in this object, with various options being set both directly though the state of the member variables (e.g. the "smoother: type") as well as indirectly (e.g. the "aggregation: type"). If you wish to have fine-grained control over the configuration of the AMG preconditioner, then you can create the parameter list using this function (which conveniently sets the null space of the operator), change the relevant settings, and use the amended parameters list as an argument to PreconditionAMG::initialize(), instead of the AdditionalData object itself.

See the documentation for the Trilinos ML package for details on what options are available for modification.

Note
Any user-defined parameters that are not in conflict with those set by this data structure will be retained.

Definition at line 67 of file trilinos_precondition_ml.cc.

## ◆ set_parameters() [2/2]

 void TrilinosWrappers::PreconditionAMG::AdditionalData::set_parameters ( Teuchos::ParameterList & parameter_list, std::unique_ptr< Epetra_MultiVector > & distributed_constant_modes, const SparseMatrix & matrix ) const

Fill in a parameter list that can be used to initialize the AMG preconditioner.

Note
Any user-defined parameters that are not in conflict with those set by this data structure will be retained.

Definition at line 188 of file trilinos_precondition_ml.cc.

## ◆ set_operator_null_space() [1/2]

 void TrilinosWrappers::PreconditionAMG::AdditionalData::set_operator_null_space ( Teuchos::ParameterList & parameter_list, std::unique_ptr< Epetra_MultiVector > & distributed_constant_modes, const Epetra_RowMatrix & matrix ) const

Configure the null space setting in the parameter_list for the input matrix based on the state of the constant_modes variable.

Definition at line 127 of file trilinos_precondition_ml.cc.

## ◆ set_operator_null_space() [2/2]

 void TrilinosWrappers::PreconditionAMG::AdditionalData::set_operator_null_space ( Teuchos::ParameterList & parameter_list, std::unique_ptr< Epetra_MultiVector > & distributed_constant_modes, const SparseMatrix & matrix ) const

Configure the null space setting in the parameter_list for the input matrix based on the state of the constant_modes variable.

Definition at line 201 of file trilinos_precondition_ml.cc.

## ◆ elliptic

Determines whether the AMG preconditioner should be optimized for elliptic problems (ML option smoothed aggregation SA, using a Chebyshev smoother) or for non-elliptic problems (ML option non- symmetric smoothed aggregation NSSA, smoother is SSOR with underrelaxation).

Definition at line 1486 of file trilinos_precondition.h.

## ◆ higher_order_elements

Determines whether the matrix that the preconditioner is built upon is generated from linear or higher-order elements.

Definition at line 1492 of file trilinos_precondition.h.

## ◆ n_cycles

Defines how many multigrid cycles should be performed by the preconditioner.

Definition at line 1498 of file trilinos_precondition.h.

## ◆ w_cycle

Defines whether a w-cycle should be used instead of the standard setting of a v-cycle.

Definition at line 1504 of file trilinos_precondition.h.

## ◆ aggregation_threshold

This threshold tells the AMG setup how the coarsening should be performed. In the AMG used by ML, all points that strongly couple with the tentative coarse-level point form one aggregate. The term strong coupling is controlled by the variable aggregation_threshold, meaning that all elements that are not smaller than aggregation_threshold times the diagonal element do couple strongly.

Definition at line 1515 of file trilinos_precondition.h.

## ◆ constant_modes

Specifies the constant modes (near null space) of the matrix. This parameter tells AMG whether we work on a scalar equation (where the near null space only consists of ones, and default value is OK) or on a vector-valued equation. For vector-valued equation problem with n_component, the provided constant_modes should fulfill the following requirements:

• n_component.size() == n_component
• n_component[*].size() == n_dof_local or n_component[*].size() == n_dof_global
• n_component[ic][id] == "idth DoF is corresponding to component ic

Definition at line 1533 of file trilinos_precondition.h.

## ◆ smoother_sweeps

Determines how many sweeps of the smoother should be performed. When the flag elliptic is set to true, i.e., for elliptic or almost elliptic problems, the polynomial degree of the Chebyshev smoother is set to smoother_sweeps. The term sweeps refers to the number of matrix-vector products performed in the Chebyshev case. In the non-elliptic case, smoother_sweeps sets the number of SSOR relaxation sweeps for post-smoothing to be performed.

Definition at line 1545 of file trilinos_precondition.h.

## ◆ smoother_overlap

Determines the overlap in the SSOR/Chebyshev error smoother when run in parallel.

Definition at line 1551 of file trilinos_precondition.h.

## ◆ output_details

If this flag is set to true, then internal information from the ML preconditioner is printed to screen. This can be useful when debugging the preconditioner.

Definition at line 1558 of file trilinos_precondition.h.

## ◆ smoother_type

Determines which smoother to use for the AMG cycle. Possibilities for smoother_type are the following:

• "Aztec"
• "IFPACK"
• "Jacobi"
• "ML symmetric Gauss-Seidel"
• "symmetric Gauss-Seidel"
• "ML Gauss-Seidel"
• "Gauss-Seidel"
• "block Gauss-Seidel"
• "symmetric block Gauss-Seidel"
• "Chebyshev"
• "MLS"
• "Hiptmair"
• "Amesos-KLU"
• "Amesos-Superlu"
• "Amesos-UMFPACK"
• "Amesos-Superludist"
• "Amesos-MUMPS"
• "user-defined"
• "SuperLU"
• "IFPACK-Chebyshev"
• "self"
• "do-nothing"
• "IC"
• "ICT"
• "ILU"
• "ILUT"
• "Block Chebyshev"
• "IFPACK-Block Chebyshev"

Definition at line 1594 of file trilinos_precondition.h.