petsc-dev 2014-04-19
Report Typos and Errors

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 the <A href="../../docs/manual.pdf#nameddest=ch_snes">SNES chapter of the users manual</A>.

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

See Also

MatDestroy(), MatMFFDSetFunctionError()

Level:advanced
Location:
src/snes/interface/noise/snesmfj2.c
Index of all SNES routines
Table of Contents for all manual pages
Index of all manual pages