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

Input Parameters#

Options Database Key#

  • -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.

See Also#

KSP: Linear System Solvers, KSPSetUp(), KSPSolve(), KSPDestroy(), KSPConvergedSkip(), KSPSetNormType(), KSPSetCheckNormIteration()

Level#

advanced

Location#

src/ksp/ksp/interface/itcreate.c


Index of all KSP routines
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Index of all manual pages