[petsc-users] Call KSP routine before each timestep

[Barry Smith]

   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