Reference documentation for deal.II version Git cb0bd54b52 2019-09-21 16:31:22 -0400

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

## Public Member Functions

AdditionalData (const unsigned int ic_fill=0, const double ic_atol=0., const double ic_rtol=1., const unsigned int overlap=0)

## Public Attributes

unsigned int ic_fill

double ic_atol

double ic_rtol

unsigned int overlap

## Detailed Description

Standardized data struct to pipe additional parameters to the preconditioner. The Trilinos IC decomposition allows for some fill-in, so it actually is a threshold incomplete Cholesky factorization. The amount of fill-in, and hence, the amount of memory used by this preconditioner, is controlled by the parameter ic_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. ic_atol is an absolute perturbation that is added to the diagonal before forming the prec, and ic_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 896 of file trilinos_precondition.h.

## Constructor & Destructor Documentation

 TrilinosWrappers::PreconditionIC::AdditionalData::AdditionalData ( const unsigned int ic_fill = 0, const double ic_atol = 0., const double ic_rtol = 1., const unsigned int overlap = 0 )

Constructor. By default, set the drop tolerance to 0, 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 IC in the parallel case makes the preconditioner a so-called additive Schwarz preconditioner.

Definition at line 464 of file trilinos_precondition.cc.

## ◆ ic_fill

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

Definition at line 920 of file trilinos_precondition.h.

## ◆ ic_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 927 of file trilinos_precondition.h.

## ◆ ic_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 933 of file trilinos_precondition.h.