# SNESConvergedDefault
Default onvergence test of the solvers for systems of nonlinear equations. 
## Synopsis
```
#include "petsc/private/snesimpl.h"   
PetscErrorCode SNESConvergedDefault(SNES snes, PetscInt it, PetscReal xnorm, PetscReal snorm, PetscReal fnorm, SNESConvergedReason *reason, void *dummy)
```
Collective on snes


## Input Parameters

- ***snes -*** the `SNES` context
- ***it -*** the iteration (0 indicates before any Newton steps)
- ***xnorm -*** 2-norm of current iterate
- ***snorm -*** 2-norm of current step
- ***fnorm -*** 2-norm of function at current iterate
- ***dummy -*** unused context



## Output Parameter

- ***reason  -*** one of


```none
   SNES_CONVERGED_FNORM_ABS       - (fnorm < abstol),
   SNES_CONVERGED_SNORM_RELATIVE  - (snorm < stol*xnorm),
   SNES_CONVERGED_FNORM_RELATIVE  - (fnorm < rtol*fnorm0),
   SNES_DIVERGED_FUNCTION_COUNT   - (nfct > maxf),
   SNES_DIVERGED_FNORM_NAN        - (fnorm == NaN),
   SNES_CONVERGED_ITERATING       - (otherwise),
   SNES_DIVERGED_DTOL             - (fnorm > divtol*snes->fnorm0)
```


where

- ***maxf -*** maximum number of function evaluations,  set with `SNESSetTolerances()`
- ***nfct -*** number of function evaluations,
- ***abstol -*** absolute function norm tolerance, set with `SNESSetTolerances()`
- ***rtol -*** relative function norm tolerance, set with `SNESSetTolerances()`
- ***divtol -*** divergence tolerance, set with `SNESSetDivergenceTolerance()`
- ***fnorm0 -*** 2-norm of the function at the initial solution (initial guess; zeroth iteration)



## Options Database Keys

- ***-snes_convergence_test default -*** see `SNESSetFromOptions()`
- ***-snes_stol -*** convergence tolerance in terms of the norm  of the change in the solution between steps
- ***-snes_atol <abstol> -*** absolute tolerance of residual norm
- ***-snes_rtol <rtol> -*** relative decrease in tolerance norm from the initial 2-norm of the solution
- ***-snes_divergence_tolerance <divtol> -*** if the residual goes above divtol*rnorm0, exit with divergence
- ***-snes_max_funcs <max_funcs> -*** maximum number of function evaluations
- ***-snes_max_fail <max_fail> -*** maximum number of line search failures allowed before stopping, default is none
- ***-snes_max_linear_solve_fail -*** number of linear solver failures before `SNESSolve()` stops





## See Also
 `SNES`, `SNESSolve()`, `SNESSetConvergenceTest()`, `SNESConvergedSkip()`, `SNESSetTolerances()`, `SNESSetDivergenceTolerance()`

## Level
intermediate

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

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex30.c.html">src/snes/tutorials/ex30.c.html</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/tutorials/ex69.c.html">src/snes/tutorials/ex69.c.html</A><BR>

## Implementations

<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/impls/vi/vi.c.html#SNESConvergedDefault_VI">SNESConvergedDefault_VI in src/snes/impls/vi/vi.c</A><BR>


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


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