Option with HYPRE and KSP

Barry Smith bsmith at mcs.anl.gov
Sun Apr 8 19:59:22 CDT 2007

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 

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.


> Thank you very much.
> Regards.

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