On 5/1/17 4:42 PM, Matthew Knepley wrote:
On Mon, May 1, 2017 at 4:27 PM, Scott Dossa <[email protected]
<mailto:[email protected]>> wrote:
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.
You should not need that since PreStep will be called at the beginning
of each step, but just in case
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/TS/TSStep.html
although using this is tricky so I do not recommend it.
If it's a projection you may need to set the PostStep and (or) PostStage
if using multistage methods
(http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/TS/TSSetPostStage.html#TSSetPostStage);
otherwise the last step may not be div free.
Barry:
Yes, this is a pressure projection method where one needs the
pressure field at each timestep to solve for the velocity field.
If it was me, I would not do it this way, but its somewhat a matter of
taste. It makes more sense to me to formulate the whole
system as a DAE, meaning time derivatives on some things (v) and not
others (p). Then use a DAE timestepper and your
fluid solver can be formulated as pressure projection using
PCFIELDSPLIT. This way, if you want to use another kind of fluid
solver, you can, whereas now you are stuck with the alternation of
projection of momentum update.
Yes, formulating it as a DAE is desirable; however, if you project it
separately you have access to significantly more time steppers.
Emil
Thanks,
Matt
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 <[email protected]
<mailto:[email protected]>> 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
<[email protected] <mailto:[email protected]>> wrote:
>
> On Mon, May 1, 2017 at 3:13 PM, Scott Dossa <[email protected]
<mailto:[email protected]>> 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
<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
--
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
