[petsc-users] PC HYPRE BoomerAMG options for nodal

[Bernardo Rocha]

No particular reason. Let's say it was the first approach I tried in an old
code.

OK, so to get it working I should use the interlaced version for the
ordering of my dofs.
It does not require too much coding on my side.

Just to know, if I wanted to insist in the non-interlaced, to keep using
Hypre/BoomerAMG from PETSc I would need to write some code in PETSc for
wrapping this feature (AMGSetDofFunc), right?

Thanks.

On Tue, Feb 14, 2017 at 11:48 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Ahh, thanks for the explanation. What a nutso API: way to general, they
> should just support interlaced and non-interlaced.
>
>   Anyways we strongly recommend using the interlaced version; for most
> calculations it gives much better locality for cache lines and cache. We
> always use interlaced. Any particular reason you use non-interlaced?
>
>   Barry
>
> > On Feb 14, 2017, at 7:17 PM, Bernardo Rocha <bernardomartinsrocha at gmail.
> com> wrote:
> >
> > Thanks a lot for the reply.
> >
> > ​From my understanding and specifically for my problem I would have to
> use the AMGSetDofFunc as follows:​
> >
> > ​nsyseq = 3;​
> > for (i=0; i<nsyseq; i++)
> > ​    ​for (k=0; k<​N​; k++)​ // N: number of nodes​
> >     {
> >     ​    ​eqnIndex[i*​N​+k] = i;
> >     }
> > HYPRE_BoomerAMGSetDofFunc(preconditioner, eqnIndex);​
> >
> > For a system of 3 PDEs (e.g. linear elasticity in 3D​) the default
> behaviour of the nodal coarsening in BoomerAMG, considers an array that is
> filled with
> >
> > eqnIndex = ​0 1 2 0 1 2 0 1 2....0 1 2
> >
> >  > HYPRE_BoomerAMGSetDofFunc
> >
> >    I could not find an indication of that this is suppose to be setting;
> it is mentioned in the users manual but I don't know what it means. It
> looks like it takes an integer array but I don't even know how long that
> array is.
> >
> >    If you figure out what it means and can add support for it we'll take
> it as a pull request.
> >
> > ​​OK Barry, I will try to specify the block size of the matrix.
> > But I'm not sure if the block size would be 3 or N (number of nodes).
> > This is my ordering of the displacements: [ux1, ux2, ..., uxN, uy1,
> uy2,...uyN, uz1, uz2, ..., uzN]
> >
> > > HYPRE_BoomerAMGSetNumFunctions
> >
> >    Set the block size of the matrix; this information is then
> transferred automatically to hypre.  Note that you can set a block size
> even for AIJ matrices.
> > ​
> > ​Best regards,
> > Bernardo​
>
>
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