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# SNESNGSSetTolerances

Sets various parameters used in convergence tests for nonlinear Gauss-Seidel `SNESNCG`

## Synopsis

    #include "petscsnes.h"
    PetscErrorCode SNESNGSSetTolerances(SNES snes, PetscReal abstol, PetscReal rtol, PetscReal stol, PetscInt maxit)

Logically Collective

## Input Parameters

- snes - the `SNES` context

- abstol - absolute convergence tolerance

- rtol - relative convergence tolerance

- stol - convergence tolerance in terms of the norm of the change in the solution between steps, || delta x || < stol*|| x ||

- maxit - maximum number of iterations

## Options Database Keys

- -snes_ngs_atol abstol - Sets abstol

- -snes_ngs_rtol rtol - Sets rtol

- -snes_ngs_stol stol - Sets stol

- -snes_max_it maxit - Sets maxit

## Notes

Use `PETSC_CURRENT` to retain the value for any parameter

All parameters must be non-negative

## Developer Note

Why can’t the values set with `SNESSetTolerances()` be used?

## See Also

SNES: Nonlinear Solvers, `SNES`, `SNESNCG`

## Level

intermediate

## Location

src/snes/impls/gs/snesgs.c

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