SNESGetLagPreconditioner — PETSc 3.21.4 documentation

Skip to main content
`Ctrl`+`K`

# SNESGetLagPreconditioner

Return how often the preconditioner is rebuilt

## Synopsis

    #include "petscsnes.h"
    PetscErrorCode SNESGetLagPreconditioner(SNES snes, PetscInt *lag)

Not Collective

## Input Parameter

- snes - the `SNES` context

## Output Parameter

- lag - -1 indicates NEVER rebuild, 1 means rebuild every time the Jacobian is computed within a single nonlinear solve, 2 means every second time the Jacobian is built etc. -2 indicates rebuild preconditioner at next chance but then never rebuild after that

## Notes

The default is 1

The preconditioner is ALWAYS built in the first iteration of a nonlinear solve unless lag is -1

## See Also

SNES: Nonlinear Solvers, `SNES`, `SNESSetTrustRegionTolerance()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`

## Level

intermediate

## Location

src/snes/interface/snes.c

Index of all SNES routines
Table of Contents for all manual pages
Index of all manual pages