Block-smoothers with variable block size

[Barry Smith]

On Mar 21, 2008, at 8:03 AM, Nicolas Tardieu wrote:

> Dear Barry,
>
> I have a few questions about inodes :
> - can the user specify the inodes sizes (it seems to me this is an  
> automatic PETSc feature to gain performance, right?)?

     No, they must be inodes, they are not arbitary
>
> - can the inodes have different sizes?

    Yes, they are what ever they are.
>
>
> Otherwise I plan to define a new matrix type MATSEQVBAIJ (VB for  
> variable block) based on MATSEQAIJ with an additional attribute  
> defining the block sizes.

    This is overkill, you will end up doing a lot more work then you  
need to!
The locations for storing the diagonal blocks is already in the  
MATSEQAIJ data structures, if you
write code to replace the MatRelax_Inode (that uses that same diagonal  
space) you are done.

    Barry


>
>
> Thanks,
>
> Nicolas
>
> 2008/3/20, Barry Smith <bsmith at mcs.anl.gov>:
>    DON"T USE GREP! Use etags
> # To access the tags in EMACS, type M-x visit-tags-table and specify
> # the file petsc/TAGS.
> # 1) To move to where a PETSc function is defined, enter M-. and the
> #     function name.
> # 2) To search for a string and move to the first occurrence,
> #     use M-x tags-search and the string.
> #     To locate later occurrences, use M-,
>
>    It may not be in petsc-2.3.3 you may need to use petsc-dev
> http://www-unix.mcs.anl.gov/petsc/petsc-as/developers/index.html
>
> it is in src/mat/impls/aij/seq/inode.c
>
>
>
>     Barry
>
>
>
> On Mar 20, 2008, at 1:52 PM, Nicolas Tardieu wrote:
>
> > Dear Barry,
> >
> > Thank you very much for your quick answer.
> > I am searching for MatRelax_Inode in PETSc src directory using grep.
> > But I just can't find it! Please note I am using 2.3.3p6
> > Could you please tell me where this routine is?
> >
> > Nicoals
> >
> > 2008/3/20, Barry Smith <bsmith at mcs.anl.gov>:
> >     Nicolas,
> >
> >      Actually we are very close to this. Check out the routine
> > MatRelax_Inode() which is for AIJ matrices.
> > For the block size it uses the inode size. If your matrix has inodes
> > that match the blocks you want
> > then everything is there already just use the PCSOR.
> >
> >      If you do not have inodes then you can mimic the  
> MatRelax_Inode()
> > code to make a new
> > routine MatPBRelax_SeqAIJ(). If you do implement this we'd love to  
> add
> > it to PETSc.
> >
> >
> >      Please let us know if you have additional questions.
> >
> >
> >     Barry
> >
> >
> >
> >
> > On Mar 20, 2008, at 1:07 PM, Nicolas Tardieu wrote:
> >
> > > Dear PETSc experts,
> > >
> > > I am currently designing a multigrid PC that needs to operate on
> > > variable block size matrices. I know PETSc does not support this
> > > feature.
> > > So, I will do it "by hand".  Neverthless I would like to be able  
> to
> > > use some smoothers like Jacobi or SOR in their block version.
> > >
> > > What is the best solution that would work both in sequential and
> > > parallel?
> > >
> > > - define some MATSHELL that handle variable block size
> > >     -> will I be able to use in some way a block Jacobi or SOR?
> > >     -> would it be possible to use CSR inside the MATSHELL and
> > > manage the variable blocks.
> > >
> > > - use a AIJ matrix and manage the blocks using some indirection
> > > mechanism and reprogram Jacobi or SOR
> > >
> > >
> > >
> > > Thank you,
> > >
> > > Nicolas
> > >
> >
> >
>
>