[petsc-users] Call KSP routine before each timestep

[Scott Dossa]

Hi All,

Matt:
Thank you! Using the application context is a good approach to pass the
vector information. Can you also direct me to which command allows TSSolve
to be only called for one timestep / start at the correct timestep? When
TSSolve() is called, it always resets to timestep 0.

Barry:
Yes, this is a pressure projection method where one needs the pressure
field at each timestep to solve for the velocity field.

I will likely have more follow up questions as I quick write this up. Thank
you both for your input.
-Scott Dossa

On Mon, May 1, 2017 at 3:32 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>    Scott -  Are you doing some kind of pressure projection method?
>
>    PETSc-developers - should this functionality be directly added to TS
> since it comes up fairly often?
>
>    Barry
>
>
>
> > On May 1, 2017, at 3:24 PM, Matthew Knepley <knepley at gmail.com> wrote:
> >
> > On Mon, May 1, 2017 at 3:13 PM, Scott Dossa <doss0032 at umn.edu> wrote:
> > Hi All,
> >
> > I'm looking to pass a vector between a KSP and TS routine. The KSP
> routine must be called before each timestep, and the solution vector is
> needed for the TS routine. Normally, TSSolve() runs over all timesteps, but
> in my case, I'd like to be able to add a routine before each timestep.
> >
> > Can someone direct me to an example script or briefly explain a case
> which shows how to control time stepping such that one could achieve
> something along the lines of:
> >
> > while (step < maxsteps+1){
> >         KSPSolve(ksp, v, p); /* solves for Vec p and passes this info
> onto TS */
> >         TSSolve(ts, u); /* only iterate for 1 timestep */
> > }
> >
> > The function TSSetPreStep() seemed promising, but it can only take TS as
> arguments which may not be sufficient to pass a global vector.
> >
> > Yes, this is the correct thing. You can
> >
> >   a) Just attach a Vec to the TS using PetscObjectCompose(), but that is
> ugly so you can
> >
> >   b) Make a context structure, and stick it in the TS using
> >
> >   http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/TS/
> TSSetApplicationContext.html
> >
> >       That is also where the KSP should go.
> >
> >   Thanks,
> >
> >     Matt
> >
> > Thank you in advance.
> > Scott Dossa
> >
> >
> >
> >
> >
> > --
> > 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
>
>
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