petsc-3.3-p7 2013-05-11

KSPDefaultConverged

Determines convergence of the iterative solvers (default code).

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

Collective on KSP

	ksp	- iterative context
	n	- iteration number
	rnorm	- 2-norm residual value (may be estimated)
	ctx	- convergence context which must be created by KSPDefaultConvergedCreate()

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

KSPDefaultConverged() 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.

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

KSP, default, convergence, residual

	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 KSPDefaultConvergedSetUIRNorm() to use the norm of (b - A*(initial guess)) as the starting point for relative norm convergence testing.