[petsc-users] how to get the differencing paramter in a matrix free formulation

[Jed Brown]

On Thu, Mar 24, 2011 at 08:25, Kontsantinos Kontzialis <
ckontzialis at lycos.com> wrote:

> Dear all,
>
>  I'm using the following function:
>
> ierr = MatMFFDGetH(sys.J, &h);
>    CHKERRQ(ierr);
>
> to get the parameter h in the formula for the jacobian-vector product, but
> it returns a value of 0. But how can that be, otherwise a division by zero
> would result.
>

"Gets the last value that was used as the differencing parameter."

http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatMFFDGetH.html

Sounds like you haven't done a multiply yet.
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