# SNESLineSearchSetPostCheck

Sets a routine to check the validity of new iterate computed by the line search routine in the Newton-based method SNESLS.

### Synopsis

    PetscErrorCode PETSCSNES_DLLEXPORT SNESLineSearchSetPostCheck(SNES snes,PetscErrorCode (*func)(SNES,Vec,Vec,Vec,void*,PetscTruth*,PetscTruth*),void *checkctx)

### Input Parameters

| snes | - nonlinear context obtained from SNESCreate()
| func | - pointer to function
| checkctx | - optional user-defined context for use by step checking routine

Collective on SNES

### Calling sequence of func

       int func (SNES snes, Vec x,Vec y,Vec w,void *checkctx, PetscTruth *changed_y,PetscTruth *changed_w)

where func returns an error code of 0 on success and a nonzero on failure.

### Input parameters for func

| snes | - nonlinear context
| checkctx | - optional user-defined context for use by step checking routine
| x | - previous iterate
| y | - new search direction and length
| w | - current candidate iterate

### Output parameters for func

| y | - search direction (possibly changed)
| w | - current iterate (possibly modified)
| changed_y | - indicates search direction was changed by this routine
| changed_w | - indicates current iterate was changed by this routine

Notes: All line searches accept the new iterate computed by the line search checking routine.

Only one of changed_y and changed_w can be PETSC_TRUE

On input w = x + y

SNESLineSearchNo() and SNESLineSearchNoNorms() (1) compute a candidate iterate u_{i+1}, (2) pass control to the checking routine, and then (3) compute the corresponding nonlinear function f(u_{i+1}) with the (possibly altered) iterate u_{i+1}.

SNESLineSearchQuadratic() and SNESLineSearchCubic() (1) compute a candidate iterate u_{i+1} as well as a candidate nonlinear function f(u_{i+1}), (2) pass control to the checking routine, and then (3) force a re-evaluation of f(u_{i+1}) if any changes were made to the candidate iterate in the checking routine (as indicated by flag=PETSC_TRUE). The overhead of this extra function re-evaluation can be very costly, so use this feature with caution!

### Keywords

SNES, nonlinear, set, line search check, step check, routine

### See Also

SNESLineSearchSet(), SNESLineSearchSetPreCheck()

Level:advanced
Location: src/snes/impls/ls/ls.c
Index of all SNES routines
Table of Contents for all manual pages
Index of all manual pages

### Examples

src/snes/examples/tutorials/ex3.c.html