:orphan:
# 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



## Options Database Keys

- ***-snes_lag_jacobian_persists <true,false> -*** sets the persistence through multiple SNES solves
- ***-snes_lag_jacobian <-*** 2,1,2,...> - sets the lag
- ***-snes_lag_preconditioner_persists <true,false> -*** sets the persistence through multiple SNES solves
- ***-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
 [](ch_snes), `SNES`, `SNESSetTrustRegionTolerance()`, `SNESSetLagPreconditioner()`, `SNESSetLagJacobianPersists()`, `SNESSetLagPreconditionerPersists()`

## Level
intermediate

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/interface/snes.c.html#SNESGetLagPreconditioner">src/snes/interface/snes.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/snes/interface/snes.c)


[Index of all SNES routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)