[petsc-users] How to set an initial guess for TS

[Fande Kong]

Thanks Jed,

I will try and let you know,

Thanks again!

Fande,

On Fri, Apr 3, 2020 at 4:29 PM Jed Brown <jed at jedbrown.org> wrote:

> Oh, you just want an initial guess for SNES?  Does it work to pull out the
> SNES and SNESSetComputeInitialGuess?
>
> Fande Kong <fdkong.jd at gmail.com> writes:
>
> > No. I am working on a transient loosely coupled multiphysics simulation.
> > Assume there are two physics problems: problem A and problem B. During
> each
> > time step, there is a Picard iteration between problem A and problem B.
> > During each Picard step, you solve problem A (or B) with the solution
> > (U_{n-1}) of the previous time step as the initial condition. In the
> Picard
> > solve stage, I know the solution (\bar{U}_{n}) of the current time step
> but
> > from the previous Picard iteration. Use \bar{U}_{n}) instead of U_{n-1}
> as
> > the initial guess for SNES will have a better convergence for me.
> >
> > Thanks,
> >
> > Fande,
> >
> >
> > On Fri, Apr 3, 2020 at 1:10 PM Jed Brown <jed at jedbrown.org> wrote:
> >
> >> This sounds like you're talking about a starting procedure for a DAE (or
> >> near-singular ODE)?
> >>
> >> Fande Kong <fdkong.jd at gmail.com> writes:
> >>
> >> > Hi All,
> >> >
> >> > TSSetSolution will set an initial condition for the current TSSolve().
> >> What
> >> > should I do if I want to set an initial guess for the current solution
> >> that
> >> > is different from the initial condition?  The initial guess is
> supposed
> >> to
> >> > be really close to the current solution, and then will accelerate my
> >> solver.
> >> >
> >> > In other words, TSSetSolution will set "U_{n-1}", and now we call
> TSSolve
> >> > to figure out "U_{n}". If I know something about "U_{n}", and I want
> to
> >> set
> >> > "\bar{U}_{n}" as the initial guess of "U_{n}" when computing "U_{n}".
> >> >
> >> >
> >> > Thanks,
> >> >
> >> > Fande,
> >>
>
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