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# SNESNCG
Nonlinear Conjugate-Gradient method for the solution of nonlinear systems. 


## Options Database Keys

- ***-snes_ncg_type <fr, prp, dy, hs, cd> -*** Choice of conjugate-gradient update parameter, default is prp.
- ***-snes_linesearch_type <cp,l2,basic> -*** Line search type.
- ***-snes_ncg_monitor -*** Print the beta values used in the ncg iteration, .



## Notes
This solves the nonlinear system of equations F(x) = 0 using the nonlinear generalization of the conjugate
gradient method.  This may be used with a nonlinear preconditioner used to pick the new search directions, but otherwise
chooses the initial search direction as F(x) for the initial guess x.

Only supports left non-linear preconditioning.

Default line search is `SNESLINESEARCHCP`, unless a nonlinear preconditioner is used with -npc_snes_type <type>, `SNESSetNPC()`, or `SNESGetNPC()` then
`SNESLINESEARCHL2` is used. Also supports the special purpose line search `SNESLINESEARCHNCGLINEAR`


## References

- **** -*** Peter R. Brune, Matthew G. Knepley, Barry F. Smith, and Xuemin Tu,"Composing Scalable Nonlinear Algebraic Solvers",
SIAM Review, 57(4), 2015



## See Also
 `SNESCreate()`, `SNES`, `SNESSetType()`, `SNESNEWTONLS`, `SNESNEWTONTR`, `SNESNGMRES`, `SNESQN`, `SNESLINESEARCHNCGLINEAR`, `SNESNCGSetType()`, `SNESLineSearchSetType()`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/impls/ncg/snesncg.c.html#SNESNCG">src/snes/impls/ncg/snesncg.c</A>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/snes/impls/ncg/snesncg.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)