petsc-3.8.4 2018-03-24
KSPSetLagNorm
Lags the residual norm calculation so that it is computed as part of the MPI_Allreduce() for computing the inner products for the next iteration. This can reduce communication costs at the expense of doing one additional iteration.
Synopsis
#include "petscksp.h"
PetscErrorCode KSPSetLagNorm(KSP ksp,PetscBool flg)
Logically Collective on KSP
Input Parameter
Options Database Keys
-ksp_lag_norm -lag the calculated residual norm
Notes
Currently only works with KSPIBCGS.
Use KSPSetNormType(ksp,KSP_NORM_NONE) to never check the norm
If you lag the norm and run with, for example, -ksp_monitor, the residual norm reported will be the lagged one.
Keywords
KSP, create, context, norms
See Also
KSPSetUp(), KSPSolve(), KSPDestroy(), KSPConvergedSkip(), KSPSetNormType(), KSPSetCheckNormIteration()
Level:advanced
Location:src/ksp/ksp/interface/itcreate.c
Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages