flexible TS implementation for user-defined timestepping

[Lisandro Dalcin]

On 9/18/07, Matthew Knepley <knepley at gmail.com> wrote:
> However, now I am forced to ask what benefit the user is really getting. He has
> to code the entire method, so we are really not providing the timestepping
> scheme. It seems that the only benefit beyond SNES is that we save some
> vectors (u^{n-k}) for him. This does not seem like much.

Indeed. If a user has the code (like me), I can benefit from having an
object being able of managing the time-steping (only for the temporal
axis), and configurable with many pre/post solve/step user-defined
routines plus a way to implement time-step size control, also through
user provided routine. All this should be seen as the highest-level
interface to TS. It does not provide very much, as all interfaces
generally do. Next, having this, he can tailor specific applications,
for linear/nonlinear implict/explicit finite diferences/ finite
elements methods.

Matt, please see my proposal as an interface change (actually
extension) to TS. It is very general, and as such, you can build
implementations in order to alleviate user to write all the (parallel)
code. But I insist that having many 'hooks' for pre/post solve/step
and time-step control in the generic TS interface would be really
useful.


> The thesis of Anders Logg (also published as papers) is very good.

I'll try to search for it ASAP. Thanks.


>
> > > > On 9/17/07, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> > > > > Current TS implementations never fited my needs. Why? My target
> > > > > application is solving incompressible NS equations with FEM and fully
> > > > > implicit schemes (trapezoidal rule with theta in [0.5, 1.0] ) and
> > > > > residual-based stabilization (SUPG/PSPG). Then I need to solve at each
> > > > > time step a nonlinear problem like F(t, u, t0, u0), where F is
> > > > > nonlinear in u. I'm surelly naive, and I could not accomodate my
> > > > > function and Jacobian code for the beuler/cn TS implementations.
> > > > >
> > > > > Futhermore, I've recently convinced some coworkers to take advance of
> > > > > SNES/TS features and my Python wrappers (petsc4py) to manage the the
> > > > > time evolution of some problems related to fluid-structure interaction
> > > > > and mesh movement (formulated as an optimization problem, only nodal
> > > > > positions change, not remeshing needed for many timesteps).
> > > > >
> > > > > In order to support those applications setups, I've wrote a new TS
> > > > > implemetation, which enables users to (almost) completely define the
> > > > > temporal evolution of their problems, with  pre/post solve/step
> > > > > methods and support for accept/reject steps and implementing timestep
> > > > > size control. Some of these features are available in some TS types,
> > > > > but not all-in-one.
> > > > >
> > > > > This code is available for review in petsc4py SVN repo (link below),
> > > > > an python example of this in action (very simple, just for testing all
> > > > > is working) is attached. Currently it only support implicit schemes
> > > > > and nonlinear problems, but I believe it can be extended to support
> > > > > explicit schemes and linear problems.
> > > > >
> > > > > http://petsc4py.googlecode.com/svn/trunk/petsc/lib/ext/src/ts/impls/implicit/user/
> > > > >
> > > > > I want to know the opinion of PETSc core developers and potential
> > > > > users ot this, and I hope anyone can provide suggestions for
> > > > > improvements. After that, I can push this to petsc-dev for general
> > > > > availability (in fact, the code is almost ready to be integrated in
> > > > > petsc).
> > > > >
> > > > > Perhaps in the long term, all this can be integrated in the generic TS
> > > > > interface if that is appropriate. Of course, this would require some
> > > > > (I hope minor) changes in TS interface, some additions, and a
> > > > > reimplementation of some default TS types
> > > > >
> > > > > Regards, and I'm waiting for your comments.
> > > > >
> > > > >
> > > > > --
> > > > > Lisandro Dalcín
> > > > > ---------------
> > > > > Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> > > > > Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> > > > > Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> > > > > PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> > > > > Tel/Fax: +54-(0)342-451.1594
> > > > >
> > > > >
> > > >
> > > >
> > > > --
> > > > What most experimenters take for granted before they begin their
> > > > experiments is infinitely more interesting than any results to which
> > > > their experiments lead.
> > > > -- Norbert Wiener
> > > >
> > >
> > >
> > > --
> > > What most experimenters take for granted before they begin their
> > > experiments is infinitely more interesting than any results to which
> > > their experiments lead.
> > > -- Norbert Wiener
> > >
> > >
> >
> >
> > --
> > Lisandro Dalcín
> > ---------------
> > Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> > Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> > Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> > PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> > Tel/Fax: +54-(0)342-451.1594
> >
> >
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which
> their experiments lead.
> -- Norbert Wiener
>
>


-- 
Lisandro Dalcín
---------------
Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
PTLC - Güemes 3450, (3000) Santa Fe, Argentina
Tel/Fax: +54-(0)342-451.1594