[petsc-users] PetscFE and TS

[Julian Andrej]

I tested a few other things and it turned out that the function added
as a dirichlet boundary condition via PetscDSAddBoundary doesn't
receive the time values correctly (PetscReal time is always 0.0).

I also see no effect adding DMTSSetIJacobianLocal vs. not setting the
jacobian function. The analytic solution i used in my attached example
is the same as in the src/ts/examples/tutorials/ex32.c.

Am i doing anything obviously wrong here? My next step would be to try
if assembling the matrices myself and writing a custom
IFunction/IJacobian which assembles the different parts of the matrix
like M and J for the stiff ODE with nontrivial mass matrix (see manual
section of TS -> F = M u' - f) but i think this should be obsolete
right?

Appreciate your help.

Regards
Julian

On Mon, Nov 7, 2016 at 10:49 AM, Julian Andrej <juan at tf.uni-kiel.de> wrote:
> Hello,
>
> i'm using PetscFE in combination with SNES and a hand written backward
> euler solver right now and like to hand that over to TS. I have been
> fiddling quite a while getting TS to work with PetscFE and have
> encountered a few unclarities.
>
> I have looked at examples which are outdated i guess
> (src/ts/examples/tutorials/ex32.c) and i am confused on how i have to
> formulate the discretization of the jacobian and the residual. It
> seems obvious to use the DMTSSetIFunctionLocal and
> DMTSSetIJacobianLocal functions because there are prepared wrappers
> from DMPlexTSComputeIFunctionFEM and DMPlexTSComputeIJacobianFEM.
>
> I need a Mass matrix for my problem, is that formed from the function
> space information or do i have to form it myself? Is there any working
> example which uses PetscFE and TS to form the DMTSSetIFunctionLocal
> and DMTSSetIJacobianLocal? (grepping the tree tells me "no"
> unfortunately).
>
> Regards
> Julian
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