petsc-3.5.2 2014-09-08
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KSPConvergedDefault

Determines convergence of the linear iterative solvers by default

Synopsis

#include "petscksp.h" 
PetscErrorCode  KSPConvergedDefault(KSP ksp,PetscInt n,PetscReal rnorm,KSPConvergedReason *reason,void *ctx)
Collective on KSP

Input Parameters

ksp - iterative context
n - iteration number
rnorm - residual norm (may be estimated, depending on the method may be the preconditioned residual norm)
ctx - convergence context which must be created by KSPConvergedDefaultCreate()

Output Parameter

positive - if the iteration has converged;
negative - if residual norm exceeds divergence threshold;
0 - otherwise.

Notes

KSPConvergedDefault() reaches convergence when rnorm < MAX (rtol * rnorm_0, abstol); Divergence is detected if rnorm > dtol * rnorm_0,

where

Use KSPSetTolerances() to alter the defaults for rtol, abstol, dtol.

Use KSPSetNormType() (or -ksp_norm_type <none,preconditioned,unpreconditioned,natural>) to change the norm used for computing rnorm

The precise values of reason are macros such as KSP_CONVERGED_RTOL, which are defined in petscksp.h.

This routine is used by KSP by default so the user generally never needs call it directly.

Use KSPSetConvergenceTest() to provide your own test instead of using this one.

Keywords

KSP, default, convergence, residual

See Also

KSPSetConvergenceTest(), KSPSetTolerances(), KSPConvergedSkip(), KSPConvergedReason, KSPGetConvergedReason(),
KSPConvergedDefaultSetUIRNorm(), KSPConvergedDefaultSetUMIRNorm(), KSPConvergedDefaultCreate(), KSPConvergedDefaultDestroy()

Level:intermediate
Location:
src/ksp/ksp/interface/iterativ.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages

rtol = relative tolerance,- . abstol = absolute tolerance.
dtol = divergence tolerance,- - rnorm_0 is the two norm of the right hand side. When initial guess is non-zero you can call KSPConvergedDefaultSetUIRNorm() to use the norm of (b - A*(initial guess)) as the starting point for relative norm convergence testing, that is as rnorm_0