petsc-3.14.5 2021-03-03
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# PCFactorSetDropTolerance

The preconditioner will use an ILU based on a drop tolerance. (Under development)

### Synopsis

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

Logically Collective on PC

### 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

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.

### 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