**petsc-master 2014-12-15**

# MatCreateSNESMF

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(). See MatCreateMFFD() for details on how the finite difference computation is done.
### Synopsis

#include "petscsnes.h"
#include "petscdm.h"
PetscErrorCode MatCreateSNESMF(SNES snes,Mat *J)

Collective on SNES and Vec

### Input Parameters

**snes ** -the SNES context

### Output Parameter

**J ** -the matrix-free matrix

### Notes

You can call SNESSetJacobian() with MatMFFDComputeJacobian() if you are using matrix and not a different
preconditioner matrix
If you wish to provide a different function to do differencing on to compute the matrix-free operator than
that provided to SNESSetFunction() then call MatMFFDSetFunction() with your function after this call.

The difference between this routine and MatCreateMFFD() is that this matrix
automatically gets the current base vector from the SNES object and not from an
explicit call to MatMFFDSetBase().

### Warning

If MatMFFDSetBase() is ever called on jac then this routine will NO longer get
the x from the SNES object and MatMFFDSetBase() must from that point on be used to
change the base vector x.

### Warning

Using a different function for the differencing will not work if you are using non-linear left preconditioning.

### See Also

MatDestroy(), MatMFFDSetFunction(), MatMFFDSetFunctionError(), MatMFFDDSSetUmin()

MatMFFDSetHHistory(), MatMFFDResetHHistory(), MatCreateMFFD(),
MatMFFDGetH(), MatMFFDRegister(), MatMFFDComputeJacobian()

**Level:**advanced

Location:src/snes/mf/snesmfj.c

Index of all SNES routines

Table of Contents for all manual pages

Index of all manual pages

### Examples

src/ts/examples/tutorials/ex15.c.html