PCFactorSetDropTolerance#

The preconditioner will use an PCILU based on a drop tolerance.

Synopsis#

#include "petscpc.h" 
PetscErrorCode PCFactorSetDropTolerance(PC pc, PetscReal dt, PetscReal dtcol, PetscInt maxrowcount)

Logically Collective

Input Parameters#

  • pc - the preconditioner context

  • dt - the drop tolerance, try from 1.e-10 to .1

  • dtcol - tolerance for column pivot, good values [0.1 to 0.01]

  • maxrowcount - the max number of nonzeros allowed in a row, best value depends on the number of nonzeros in row of original matrix

Options Database Key#

  • -pc_factor_drop_tolerance <dt,dtcol,maxrowcount> - Sets drop tolerance

Note#

There are NO default values for the 3 parameters, you must set them with reasonable values for your matrix. We don’t know how to compute reasonable values.

See Also#

KSP: Linear System Solvers, PCILU

Level#

intermediate

Location#

src/ksp/pc/impls/factor/factor.c

Implementations#

PCFactorSetDropTolerance_Factor() in src/ksp/pc/impls/factor/factimpl.c
PCFactorSetDropTolerance_ILU() in src/ksp/pc/impls/factor/ilu/ilu.c

Index of all PC routines
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Index of all manual pages