petsc-3.14.5 2021-03-03
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# SNESGetLagPreconditioner

Indicates 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

### Options Database Keys

| -snes_lag_jacobian_persists <true,false> | - sets the persistence
| -snes_lag_jacobian < | - 2,1,2,...> - sets the lag
| -snes_lag_preconditioner_persists <true,false> | - sets the persistence
| -snes_lag_preconditioner < | - 2,1,2,...> - sets the lag

### Notes

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

### See Also

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