MatSNESMFSetType

Sets the method that is used to compute the differencing parameter for finite differene matrix-free formulations.

#include "petscsnes.h"   
int MatSNESMFSetType(Mat mat,MatSNESMFType ftype)

	mat	- the "matrix-free" matrix created via MatCreateSNESMF(), or MatCreateMF() or MatSetType(mat,MATMFFD);
	ftype	- the type requested

For example, such routines can compute h for use in Jacobian-vector products of the form

F(x+ha) - F(x) F'(u)a ~= ---------------- h