[petsc-users] Differencing parameter

[Jed Brown]

On Tue, Mar 29, 2011 at 08:07, Kontsantinos Kontzialis <
ckontzialis at lycos.com> wrote:

>  When should I call MatMFFDGeth in order to get the differencing parameter?
> I call it after SNESSolve but I get zero for h.
>

I suspect you are calling this function on a matrix of the wrong type (and,
because this function does not check types properly, returning nonsense
bytes that happen to represent a very small floating point value). Try
calling

    ierr = SNESGetJacobian(snes,&mat,0,0,0);CHKERRQ(ierr);
    ierr = MatMFFDGetH(mat,&h);CHKERRQ(ierr);
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