petsc-3.5.4 2015-05-23

SNESMatrixFreeCreate2

Creates a matrix-free matrix context for use with a SNES solver. This matrix can be used as the Jacobian argument for the routine SNESSetJacobian().

Synopsis

#include "petscsnes.h"   
PetscErrorCode  SNESDefaultMatrixFreeCreate2(SNES snes,Vec x,Mat *J)

Input Parameters

snes -the SNES context

x -vector where SNES solution is to be stored.

Output Parameter

J -the matrix-free matrix

Notes

The matrix-free matrix context merely contains the function pointers and work space for performing finite difference approximations of Jacobian-vector products, J(u)*a, via

      J(u)*a = [J(u+h*a) - J(u)]/h,

  where by default

       h = error_rel*u'a/||a||^2                        if  |u'a| > umin*||a||_{1}

         = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2   otherwise

  where

       error_rel = square root of relative error in

                   function evaluation

       umin = minimum iterate parameter

  Alternatively, the differencing parameter, h, can be set using

  Jorge's nifty new strategy if one specifies the option

         -snes_mf_jorge

The user can set these parameters via MatMFFDSetFunctionError(). See Users-Manual: ch_snes for details

The user should call MatDestroy() when finished with the matrix-free matrix context.

Options Database Keys

 -snes_mf_err <error_rel>

 -snes_mf_unim <umin>

 -snes_mf_compute_err

 -snes_mf_freq_err <freq>

 -snes_mf_jorge

Keywords

SNES, default, matrix-free, create, matrix