KSPCGUseSingleReduction#

Merge the two inner products needed in KSPCG into a single MPI_Allreduce() call.

Synopsis#

#include "petscksp.h" 
PetscErrorCode KSPCGUseSingleReduction(KSP ksp, PetscBool flg)

Logically Collective

Input Parameters#

  • ksp - the iterative context

  • flg - turn on or off the single reduction

Options Database Key#

  • -ksp_cg_single_reduction - Merge inner products into single MPI_Allreduce()

Notes#

The algorithm used in this case is described as Method 1 in [DAzevedoER93]. V. Eijkhout credits the algorithm initially to Chronopoulos and Gear.

It requires two extra work vectors than the conventional implementation in PETSc.

See also KSPPIPECG, KSPPIPECR, and KSPGROPPCG that use non-blocking reductions. Pipelined Krylov Methods,

References#

DAzevedoER93

EF D’Azevedo, VL Eijkhout, and CH Romine. Conjugate gradient algorithms with reduced synchronization overhead on distributed memory multiprocessors. Computer Science Technical Report CS-93-185, University of Tennessee, Knoxville, 1993.

See Also#

KSP: Linear System Solvers, Pipelined Krylov Methods, KSP, KSPCG, KSPGMRES, KSPPIPECG, KSPPIPECR, and KSPGROPPCG

Level#

intermediate

Location#

src/ksp/ksp/impls/cg/cgtype.c

Implementations#

KSPCGUseSingleReduction_CG() in src/ksp/ksp/impls/cg/cg.c

Index of all KSP routines
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Index of all manual pages