[petsc-users] Flexiable AIJ matrix for nonzeros -- hash table version

[Gong Ding]

>     We really appreciate the work you've done on this, but
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> 1) we can't accept patches to the released version of PETSc since that is likely outdated compared to petsc-dev. We'd like all patches that can be applied directly to petsc-dev http://www.mcs.anl.gov/petsc/petsc-as/developers/index.html#Sending_patches_to_update_the_

I did the edit based on petsc-3.1. OK, I will shift to petsc-dev.
Our company always use Git, so I need to spend some time on Mercurial.   
 
 
> 2) as Jed mentioned in an earlier email. It is sort of over-kill to provide an entire new matrix class with the hash table stuff.  If instead it was provided as runtime optional support directly in the SeqAIJ matrices that would be simpler to maintain and for people to use. So you could just add the additional data structure inside the Mat_SeqAIJ and then have MatSetValues_SeqAIJ() use the hash table directly when appropriate. 

That's great if hash table can be introduced in AIJ. 
I used to think that your guys reject any changes to basic petsc objects.