dolfin team mailing list archive

["Andy Ray Terrel" <aterrel@xxxxxxxxxxxx>]

On Wed, Sep 24, 2008 at 8:36 PM, Nuno David Lopes <ndl@xxxxxxxxxxxxxx> wrote:
> Is there a simple way of setting an initial guess for an Iterative
> LinearSolver?
> In Umfpack and PETSc the default initial guess is the zero vector right?

Not necessarily:
http://www-unix.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/KSP/KSPSetInitialGuessNonzero.html


> For time dependent problems it would  be great if one could use the last step
> solutions as the initial guess.
> I was thinking of something like
> -----------------------------------------
> solver.solve(A,x_(n+1),x_n,b)
> -----------------------------------------
> where x_n is the initial guess for the iterative solver.
>
> Also another doubt, (i'm guessing  that is my math ignorance only)
> is it usual that  PETSc::gmres with hypre::amg preconditioner doesn't work.
> (After reading that it is so powerfull...)
> In a Stokes 566000^2  subsystem it simply blows up with all of the  RAM memory
> (16Gb).
> (I tried it with simpler problems but with bigger systems   and it worked
> perfectly, converging in <10 iterations.)
>
> Sorry for some disturbance in  the troubled-hard-development times you are
> having and thanks again.
>
> --
> Nuno David Lopes
> http://ptmat.ptmat.fc.ul.pt/%7Endl/
>
> Wed Sep 24 18:58:27 WEST 2008
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