dolfin team mailing list archive

[Nuno David Lopes <ndl@xxxxxxxxxxxxxx>]

On Thursday 25 September 2008, you wrote:
> Nuno David Lopes 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?
Sorry I didn't meant Umfpack....Krylov Solver (gmres) via uBLAS backend or 
PETSc 
> At the moment, yes (note the UMFPACK is an LU solver, so an initial
> guess doesn't do anything).
>
> It's very simple, and I've been meaning to add an option for using an
> initial guess. It's also useful for Newton solvers. I'll add something
> in the next few days.
Great!!!!!!!!!!!!! 


> Garth
>
> > 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

e-mail:ndl@xxxxxxxxxxxxxx        (FCUL/CMAF)
           nlopes@xxxxxxxxxxxxxxx    (ISEL)
http://ptmat.ptmat.fc.ul.pt/%7Endl/ 

Thu Sep 25 14:50:02 WEST 2008