dolfin team mailing list archive

[Nuno David Lopes <ndl@xxxxxxxxxxxxxx>]

Well, in my stokes/uzawa codes I get much worst times, more iterations and the 
global error diverges. (But I've to think a little more about it, even in the 
first iteration i get different times.) So they don't work anymore. :(

So I tested with convection-difusion and please take a look at the solutions.   
Even with the LU solver.

On Friday 26 September 2008, Garth N. Wells wrote:
> Garth N. Wells 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?
> >
> > 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.
>
> I've added this, although it's untested. Let me know if it works ok.
>
> Garth
>
> > 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.
> >
> > _______________________________________________
> > DOLFIN-dev mailing list
> > DOLFIN-dev@xxxxxxxxxx
> > http://www.fenics.org/mailman/listinfo/dolfin-dev



-- 
Nuno David Lopes

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

Fri Sep 26 10:20:36 WEST 2008