HYPRE with multiple variables

[Nicolas Bathfield]

Dear Barry,

Using MatSetBlockSize(A,5) improved my results greatly. Boomemramg is now
solving the system of equations.
Still, the equations I solve are coupled, and my discretization scheme is
meant for a non-segregated solver. As a consequence (I believe), boomeramg
still diverges. I would therefore like to use the nodal relaxation in
boomeramg (the hypre command is HYPRE_BOOMERAMGSetNodal) in order to
couple the coarse grid choice for all my variables.

How can I achieve this from PETSc?

Best regards,

Nicolas

>
>   From PETSc MPIAIJ matrices you need to set the block size of the matrix
> with MatSetBlockSize(A,5) after you have called MatSetType() or
> MatCreateMPIAIJ(). Then HYPRE_BoomerAMGSetNumFunctions() is automatically
> called by PETSc.
>
>    Barry
>
> The reason this is done this way instead of as
> -pc_hypre_boomeramg_block_size <bs> is the idea that hypre will use the
> properties of the matrix it is given in building the preconditioner so
> the user does not have to pass those properties in seperately directly
> to hypre.
>
>
> On Fri, 13 Apr 2007, Shaman Mahmoudi wrote:
>
>> Hi,
>>
>> int HYPRE_BoomerAMGSetNumFunctions (.....)
>>
>> sets the size of the system of PDEs.
>>
>> With best regards, Shaman Mahmoudi
>>
>> On Apr 13, 2007, at 2:04 PM, Shaman Mahmoudi wrote:
>>
>> > Hi Nicolas,
>> >
>> > You are right. hypre has changed a lot since the version I used.
>> >
>> > I found this interesting information:
>> >
>> > int HYPRE_BOOMERAMGSetNodal(....)
>> >
>> > Sets whether to use the nodal systems version. Default is 0.
>> >
>> > Then information about smoothers:
>> >
>> > One interesting thing there is this,
>> >
>> > HYPRE_BoomerAMGSetDomainType(....)
>> >
>> > 0 - each point is a domain (default)
>> > 1 each node is a domain (only of interest in systems AMG)
>> > 2 ....
>> >
>> > I could not find how you define the nodal displacement ordering. But
>> it
>> > should be there somewhere.
>> >
>> > I read the reference manual for hypre 2.0
>> >
>> > With best regards, Shaman Mahmoudi
>> >
>> >
>> > On Apr 13, 2007, at 1:40 PM, Nicolas Bathfield wrote:
>> >
>> > > Dear Shaman,
>> > >
>> > > As far as I could understand, there is a BoomerAMG?s systems AMG
>> version
>> > > available. This seems to be exactly what I am looking for, but I
>> just
>> > > don't know how to access it, either through PETSc or directly.
>> > >
>> > > Best regards,
>> > >
>> > > Nicolas
>> > >
>> > > > Hi,
>> > > >
>> > > > You want to exploit the structure of the model?
>> > > > As far as I know, boomeramg can not treat a set of rows or blocks
>> as
>> > > > a molecule,  a so called block-smoother?
>> > > > ML 2.0 smoothed aggregation does support it.
>> > > >
>> > > > With best regards, Shaman Mahmoudi
>> > > >
>> > > > On Apr 13, 2007, at 10:45 AM, Nicolas Bathfield wrote:
>> > > >
>> > > > > Hi,
>> > > > >
>> > > > > I am solving the Navier-stokes equations and try to use Hypre as
>> > > > > preconditioner.
>> > > > > Until now, I used PETSc as non-segregated solver and it worked
>> > > > > perfectly.
>> > > > > Things got worse when I decided to use Boomeramg (Hypre).
>> > > > > As I solve a system of PDEs,  each cell is represented by 5 rows
>> in my
>> > > > > matrix (I solve for 5 variables). PETSc handles that without
>> problem
>> > > > > apparently, but the coarsening scheme of Boomeramg needs more
>> input in
>> > > > > order to work properly.
>> > > > >
>> > > > > Is there an option in PETSc to tell HYPRE that we are dealing
>> with a
>> > > > > system of PDEs? (something like:  -pc_hypre_boomeramg_...)
>> > > > >
>> > > > >
>> > > > > Thanks for your help.
>> > > > >
>> > > > > Best regards,
>> > > > >
>> > > > > Nicolas
>> > > > >
>> > > > >
>> > > > > --
>> > > > > Nicolas BATHFIELD
>> > > > > Chalmers University of Technology
>> > > > > Shipping and Marine Technology
>> > > > > phone: +46 (0)31 772 1476
>> > > > > fax:   +46 (0)31 772 3699
>> > > > >
>> > > >
>> > > >
>> > >
>> > >
>> > > --
>> > > Nicolas BATHFIELD
>> > > Chalmers University of Technology
>> > > Shipping and Marine Technology
>> > > phone: +46 (0)31 772 1476
>> > > fax:   +46 (0)31 772 3699
>> > >
>> >
>>


-- 
Nicolas BATHFIELD
Chalmers University of Technology
Shipping and Marine Technology
phone: +46 (0)31 772 1476
fax:   +46 (0)31 772 3699