# SNESLineSearchQuadratic

Performs a quadratic line search.

### Synopsis

    PetscErrorCode PETSCSNES_DLLEXPORT SNESLineSearchQuadratic(SNES snes,void *lsctx,Vec x,Vec f,Vec g,Vec y,Vec w,PetscReal fnorm,PetscReal *ynorm,PetscReal *gnorm,PetscTruth *flag)

Collective on SNES and Vec

### Input Parameters

| snes | - the SNES context
| lsctx | - optional context for line search (not used here)
| x | - current iterate
| f | - residual evaluated at x
| y | - search direction
| w | - work vector
| fnorm | - 2-norm of f

### Output Parameters

| g | - residual evaluated at new iterate w
| w | - new iterate (x + alpha*y)
| gnorm | - 2-norm of g
| ynorm | - 2-norm of search length
| flag | - PETSC_TRUE if line search succeeds; PETSC_FALSE on failure.

### Options Database Keys

| -snes_ls quadratic | - Activates SNESLineSearchQuadratic()
| -snes_ls_alpha <alpha> | - Sets alpha
| -snes_ls_maxstep <max> | - Sets maxstep
| -snes_ls_steptol <steptol> | - Sets steptol, this is the minimum step size that the line search code will accept; min p[i]/x[i] < steptol. The -snes_stol <stol> is the minimum step length the default convergence test will use and is based on 2-norm(p) < stol*2-norm(x) Notes: Use SNESLineSearchSet() to set this routine within the SNESLS method.

### Keywords

SNES, nonlinear, quadratic, line search

### See Also

SNESLineSearchCubic(), SNESLineSearchNo(), SNESLineSearchSet(), SNESLineSearchNoNorms()

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