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

[Fande Kong]

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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