Re: Option with HYPRE and KSP

["Ben Tay" <zonexo@xxxxxxxxx>]

Ok thank you very much

On 4/9/07, Barry Smith <bsmith@xxxxxxxxxxx> wrote:

On Mon, 9 Apr 2007, Ben Tay wrote:

> Hi,
>
> I am solving a poisson eqn and using hypre as a preconditioner has greatly
> increased the speed. I am trying to do some more tuning and I have some
> questions:
>
> 1. Is boomerAMG the only option?

Yes, but all will suck on the poisson compared to boomeramg, so stick to
boomer

What are the other hypre conditioners
> available? Is there any documentation somewhere?

Run with -help and check the hypre users manual

>Is hypre just a
> preconditioner or can it be a solver as well?

Run with -ksp_type richardson to use it as a "solver"
>
> 2. what does the preonly in ksp_type mean? Is the eqns solved?

  It means apply the preconditioner ONCE, unless the preconditioner is
a direct solver it does not solve the equations. Richardson means run
some number of iterations of the preconditioner and can solve the equations

>
> 3. why can't I use bcgs  or bicg with hypre?

  hypre doesn't support applying the transpose of the preconditioner that
bcgs and bicg need?


> Also, can cg be used for
> non-symmetric matrix. It seems to work.

Sometimes it works, but it is dangerous and not worth risking.

  Barry

>
> Thank you very much.
>
> Regards.
>