petsc-3.6.4 2016-04-12

MatMFFDSetFunctionError

Sets the error_rel for the approximation of matrix-vector products using finite differences.

Synopsis

#include "petscmat.h"   
PetscErrorCode  MatMFFDSetFunctionError(Mat mat,PetscReal error)

Logically Collective on Mat

Input Parameters

	mat	- the matrix free matrix created via MatCreateMFFD() or MatCreateSNESMF()
	error_rel	- relative error (should be set to the square root of the relative error in the function evaluations)

Options Database Keys

Notes

The default matrix-free matrix-vector product routine computes

     F'(u)*a = [F(u+h*a) - F(u)]/h where
     h = error_rel*u'a/||a||^2                        if  |u'a| > umin*||a||_{1}
       = error_rel*umin*sign(u'a)*||a||_{1}/||a||^2   else

Keywords