dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

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.  
>
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