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, secant, 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 lambda 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 (that is lambda) 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.

In certain situations SNESLineSearchApply() may directly set a SNESConvergedReason in the SNES object so one should always check this value immediately after the call to SNESLineSearchApply().