[petsc-dev] DMCreateMatrix_Moab vs. DMCreateMatrix

[Tim Tautges]

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?

- tim

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              Tim Tautges            Argonne National Laboratory
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