SNESLineSearchApply#

Computes the line-search update.

Synopsis#

#include "petscsnes.h" 
PetscErrorCode SNESLineSearchApply(SNESLineSearch linesearch, Vec X, Vec F, PetscReal *fnorm, Vec Y)

Collective

Input Parameter#

linesearch - The line search context

Input/Output Parameters#

X - The current solution, on output the new solution
F - The current function value, on output the new function value at the solution value X
fnorm - The current norm of F, on output the new norm of F
Y - The current search direction, on output the direction determined by the linesearch, i.e. Xnew = Xold - lambda*Y

Options Database Keys#

-snes_linesearch_type - basic (or equivalently none), bt, l2, cp, nleqerr, bisection, shell
-snes_linesearch_monitor [:filename] - Print progress of line searches
-snes_linesearch_damping - The linesearch damping parameter, default is 1.0 (no damping)
-snes_linesearch_norms - Turn on/off the linesearch norms computation (SNESLineSearchSetComputeNorms())
-snes_linesearch_keeplambda - Keep the previous search length as the initial guess
-snes_linesearch_max_it - The number of iterations for iterative line searches

Notes#

This is typically called from within a SNESSolve() implementation in order to help with convergence of the nonlinear method. Various SNES types use line searches in different ways, but the overarching theme is that a line search is used to determine an optimal damping parameter of a step at each iteration of the method. Each application of the line search may invoke SNESComputeFunction() several times, and therefore may be fairly expensive.