:orphan:
# SNESLINESEARCHBT
Backtracking line search. This line search finds the minimum of a polynomial fitting of the L2 norm of the
function or the objective function if it is provided with `SNESSetObjective()`.
If this fit does not satisfy the conditions for progress, the interval shrinks
and the fit is reattempted at most max_it times or until lambda is below minlambda.


## Options Database Keys

- ***-snes_linesearch_alpha <1e-4> -*** slope descent parameter
- ***-snes_linesearch_damping <1.0> -*** initial step length
- ***-snes_linesearch_maxstep <length> -*** if the length the initial step is larger than this then the
step is scaled back to be of this length at the beginning of the line search
- ***-snes_linesearch_max_it <40> -*** maximum number of shrinking step
- ***-snes_linesearch_minlambda <1e-12> -*** minimum step length allowed
- ***-snes_linesearch_order <1,2,3> -*** order of the approximation. With order 1, it performs a simple backtracking without any curve fitting





## Note
This line search will always produce a step that is less than or equal to, in length, the full step size.


## Reference

- ***- * -*** "Numerical Methods for Unconstrained Optimization and Nonlinear Equations" by Dennis and Schnabel, page 325.



## See Also
 `SNESLineSearch`, `SNESLineSearchType`, `SNESLineSearchCreate()`, `SNESLineSearchSetType()`

## Level
advanced

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/snes/linesearch/impls/bt/linesearchbt.c.html#SNESLINESEARCHBT">src/snes/linesearch/impls/bt/linesearchbt.c</A>


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