[petsc-dev] DMCreateMatrix_Moab vs. DMCreateMatrix

[Matthew Knepley]

On Tue, Mar 5, 2013 at 11:03 AM, Tim Tautges <tautges at mcs.anl.gov> wrote:

> Hi all,
>   In a previous pull request, Jed suggested "Unless you have grand plans
> for matrices "in MOAB", you should avoid masquerading as a matrix format
> and just implement DMCreateMatrix_MOAB (preferring a BAIJ matrix, it
> seems)."  But, in the documentation for many specific matrix types (I
> checked BAIJ and AIJ), it says "For good matrix assembly performance the
> user should preallocate the matrix storage by setting the parameters d_nz
> (or d_nnz) and o_nz (or o_nnz). By setting these parameters accurately,
> performance can be increased by more than a factor of 50."  So if a matrix
> can be created DMCreateMatrix (which passes just the dm and a Mat*), how
> does one efficiently create this matrix generically without calling the
> type-specific function?  Do you set options for nz and nnz, or are there
> MatSet-type functions for setting these?


The DM is supposed to know both the topology and data layout, which allows
you to calculate the sparsity.

   Matt


>
> - tim
>
> --
> ==============================**==============================**====
> "You will keep in perfect peace him whose mind is
>   steadfast, because he trusts in you."               Isaiah 26:3
>
>              Tim Tautges            Argonne National Laboratory
>          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>  phone (gvoice): (608) 354-1459      1500 Engineering Dr.
>             fax: (608) 263-4499      Madison, WI 53706
>
>


-- 
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
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