KSPSetDiagonalScale#

Tells KSP to symmetrically diagonally scale the system before solving. This actually CHANGES the matrix (and right hand side).

Synopsis#

#include "petscksp.h" 
#include "petscmat.h" 
PetscErrorCode KSPSetDiagonalScale(KSP ksp, PetscBool scale)

Logically Collective

Input Parameters#

ksp - the KSP context
scale - PETSC_TRUE or PETSC_FALSE

Options Database Keys#

-ksp_diagonal_scale - perform a diagonal scaling before the solve
-ksp_diagonal_scale_fix - scale the matrix back AFTER the solve

Notes#

Scales the matrix by D^(-1/2) A D^(-1/2) [D^(1/2) x ] = D^(-1/2) b where D_{ii} is 1/abs(A_{ii}) unless A_{ii} is zero and then it is 1.

BE CAREFUL with this routine: it actually scales the matrix and right hand side that define the system. After the system is solved the matrix and right hand side remain scaled unless you use KSPSetDiagonalScaleFix()

This should NOT be used within the SNES solves if you are using a line search.

If you use this with the PCType PCEISENSTAT preconditioner than you can use the PCEisenstatSetNoDiagonalScaling() option, or -pc_eisenstat_no_diagonal_scaling to save some unneeded, redundant flops.

Level#

advanced

Location#

src/ksp/ksp/interface/itfunc.c

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Index of all manual pages