KSPGMRESSetOrthogonalization

Sets the orthogonalization routine used by GMRES and FGMRES.

Synopsis

#include "petscksp.h"  
int KSPGMRESSetOrthogonalization(KSP ksp,int (*fcn)(KSP,int))

Collective on KSP

Input Parameters

	ksp	- iterative context obtained from KSPCreate
	fcn	- orthogonalization function

Calling Sequence of function

  errorcode = int fcn(KSP ksp,int it);

  it is one minus the number of GMRES iterations since last restart;

   i.e. the size of Krylov space minus one

Notes

Several orthogonalization routines are predefined, including

KSPGMRESModifiedGramSchmidtOrthogonalization()

KSPGMRESUnmodifiedGramSchmidtOrthogonalization() - NOT recommended; however, for some problems, particularly when using parallel distributed vectors, this may be significantly faster. Default.

KSPGMRESIROrthogonalization() - iterative refinement version of KSPGMRESUnmodifiedGramSchmidtOrthogonalization(), which may be more numerically stable.

Options Database Keys

	-ksp_gmres_unmodifiedgramschmidt	- Activates KSPGMRESUnmodifiedGramSchmidtOrthogonalization() (default)
	-ksp_gmres_modifiedgramschmidt	- Activates KSPGMRESModifiedGramSchmidtOrthogonalization()
	-ksp_gmres_irorthog	- Activates KSPGMRESIROrthogonalization()

Keywords

KSP, GMRES, set, orthogonalization, Gram-Schmidt, iterative refinement