Reference documentation for deal.II version 8.1.0
Public Member Functions | Public Attributes | List of all members
TrilinosWrappers::PreconditionILU::AdditionalData Struct Reference

#include <trilinos_precondition.h>

Public Member Functions

 AdditionalData (const unsigned int ilu_fill=0, const double ilu_atol=0., const double ilu_rtol=1., const unsigned int overlap=0)
 

Public Attributes

unsigned int ilu_fill
 
double ilu_atol
 
double ilu_rtol
 
unsigned int overlap
 

Detailed Description

Standardized data struct to pipe additional parameters to the preconditioner. The Trilinos ILU decomposition allows for some fill-in, so it actually is a threshold incomplete LU factorization. The amount of fill-in, and hence, the amount of memory used by this preconditioner, is controlled by the parameter ilu_fill, which specifies this as a double. When forming the preconditioner, for certain problems bad conditioning (or just bad luck) can cause the preconditioner to be very poorly conditioned. Hence it can help to add diagonal perturbations to the original matrix and form the preconditioner for this slightly better matrix. ilu_atol is an absolute perturbation that is added to the diagonal before forming the prec, and ilu_rtol is a scaling factor $rtol \geq 1$. The last parameter specifies the overlap of the partitions when the preconditioner runs in parallel.

Definition at line 811 of file trilinos_precondition.h.

Constructor & Destructor Documentation

TrilinosWrappers::PreconditionILU::AdditionalData::AdditionalData ( const unsigned int  ilu_fill = 0,
const double  ilu_atol = 0.,
const double  ilu_rtol = 1.,
const unsigned int  overlap = 0 
)

Constructor. By default, the level of extra fill-ins is set to be zero (just use the matrix structure, do not generate any additional fill-in), the tolerance level are 0 and 1, respectively, and the overlap in case of a parallel execution is zero. This overlap in a block-application of the ILU in the parallel case makes the preconditioner a so-called additive Schwarz preconditioner.

Member Data Documentation

unsigned int TrilinosWrappers::PreconditionILU::AdditionalData::ilu_fill

This specifies the amount of additional fill-in elements besides the sparse matrix structure. When ilu_fill is large, this means that many fill-ins will be added, so that the ILU preconditioner comes closer to a (direct) sparse LU decomposition. Note, however, that this will drastically increase the memory requirement, especially when the preconditioner is used in 3D.

Definition at line 855 of file trilinos_precondition.h.

double TrilinosWrappers::PreconditionILU::AdditionalData::ilu_atol

This specifies the amount of an absolute perturbation that will be added to the diagonal of the matrix, which sometimes can help to get better preconditioners.

Definition at line 865 of file trilinos_precondition.h.

double TrilinosWrappers::PreconditionILU::AdditionalData::ilu_rtol

This specifies the factor by which the diagonal of the matrix will be scaled, which sometimes can help to get better preconditioners.

Definition at line 874 of file trilinos_precondition.h.

unsigned int TrilinosWrappers::PreconditionILU::AdditionalData::overlap

This determines how large the overlap of the local matrix portions on each processor in a parallel application should be.

Definition at line 883 of file trilinos_precondition.h.


The documentation for this struct was generated from the following file: