[petsc-users] Matrix Construction Question

[Adam Byrd]

Actually, it's quite sparse. In the 3600x3600 there are only just 4 nonzero
entries in each row. This means it's 99.9% empty. My smaller 6x6 example is
dense, but it's only practice building and manipulating matrices.

Respectfully,
Adam

On Tue, Jun 28, 2011 at 5:55 PM, Matthew Knepley <knepley at gmail.com> wrote:

> It sounds like you have a dense matrix (from your example). Is this true?
> If so, you should use Elemental (on Google Code).
>
>   Thanks,
>
>      Matt
>
> On Tue, Jun 28, 2011 at 8:55 AM, Adam Byrd <adam1.byrd at gmail.com> wrote:
>
>> Hi,
>>
>> I'm rather new to PETSc and trying to work out the best way to create and
>> fill a large sparse matrix distributed over many processors. Currently, my
>> goal is to create a 3600x3600 matrix in units of 12x12 blocks with several
>> blocks on any given node. I'd like to create the matrix in such a way that
>> each node only holds the information in it's handful of blocks and not the
>> entire matrix. Eventually, this matrix is to be inverted (I know, inversion
>> should be avoided, but as this is a Hamiltonian matrix from which I need the
>> Green's function, I'm unaware of a way to forgo carrying out the inversion).
>> Additionally, the values will be changed slightly and the matrix will be
>> repeatedly inverted. It's structure will remain the same. In order to learn
>> how to do this is I am starting with a small 6x6 matrix broken into four 3x3
>> blocks and distributed one block per node. I've been able to create a local
>> 3x3 matrix on each node, with it's own values, and with the global
>> row/column IDs correctly set to [0, 1, 2] or [3, 4, 5] depending on where
>> the block is in the matrix. My problem manifests when I try to create the
>> larger matrix from the individual smaller ones. When the matrix is
>> constructed I'm trying to use MatSetValues and having each node pass in it's
>> 3x3 block. I end up with an error that the sum of local lengths 12x12 does
>> not match the global length 6x6. It appears as though this is from passing
>> in four 3x3s and the program interpreting that as a 12x12 instead of as a
>> 6x6 with the blocks in a grid.
>>
>> My question is then: is it possible to fill a matrix as a grid of blocks,
>> or can I only fill it in groups of rows or columns? Also, am I approaching
>> this problem the correct way, or are there more efficient ways of building
>> this matrix with the ultimate goal of inverting it?
>>
>> I have included my copy of a modified example if it helps. I do apologize
>> if this is answered somewhere in the documentation, I have been unable to
>> find a solution.
>>
>> Respectfully,
>> Adam
>>
>
>
>
> --
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110628/967a1532/attachment.htm>