[petsc-users] petsc4py: reuse setup for multiple solver calls?

[Robert Speck]

Hi!

I would like to use petsc4py for my own Python library. Installation
went well, first tests (serial and parallel) look good.

Here is what I want to do: I have my own time-stepping playground and I
want petsc4py to be one of my backbones for the data types and (linear
or non-linear, serial or parallel) solvers. I don't want to use PETSc's
time-steppers, at least not for now. So, I saw in some examples, in
particular the ones shipped with petsc4py, that the standard way of
running one of PETSc's solvers is a bunch of setup routines, then
setting the right-hand side and solve.

Now, I don't want to rerun the whole setup part each time I call the
solver. I know that I can change the right-hand side without having to
do so, but what if I change a parameter of my operator like, say, the
time-step size or some material parameter?

Take the simplest case: Say I have my own implicit Euler written in
Python. I know the right-hand side F of my ODE, so in each step I want
to solve "I - dt*F". But the time-step changes every now and then, so I
cannot pre-assemble everything once and for all (or I don't want to).
What do I need to rerun before I can use the solver again, what can I
reuse? Could I just assemble F and combine it with the identity and the
parameter dt right before I call the solver? How would that look like?

I'm pretty new to PETSc and to petsc4py, so please forgive any stupidity
or ignorance in these questions. I'm happy to take any advice, links to
examples or previous questions. Thanks!

Kind regards
-Robert-

--
Dr. Robert Speck
Juelich Supercomputing Centre
Institute for Advanced Simulation
Forschungszentrum Juelich GmbH
52425 Juelich, Germany

Tel: +49 2461 61 1644
Fax: +49 2461 61 6656

Email:   r.speck at fz-juelich.de
Website: http://www.fz-juelich.de/ias/jsc/speck_r
PinT:    http://www.fz-juelich.de/ias/jsc/pint



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