petsc-3.7.7 2017-09-25
   
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