MATMPIAIJ vs MATMPIBAIJ

[jarunan at ascomp.ch]

Thank you very much, Jed.
I understand it now.

Jarunan


Quoting Jed Brown <jed at 59A2.org>:

> On Thu, 03 Dec 2009 11:40:14 +0100, jarunan at ascomp.ch wrote:
>> Could I use BAIJ format if my block size is not the same in each
>> block?
>
> No, but AIJ uses Inodes when you have adjacent rows with the same
> nonzero pattern, this gives some advantages of BAIJ in sparse matrix
> kernels (MatMult, MatSolve, MatRelax).
>
>> At the end of the day, would these 2 structures of matrix affect
>> differently in solving performance such as speed up?
>
> This is very dependent on the preconditioner.  BAIJ reduces memory usage
> from 12 bytes per nonzero to about 8 (assuming scalar=double, 32-bit
> indices), and makes memory access slightly more regular.  Despite AIJ
> using Inodes, I frequently see BAIJ being faster by this ratio (8/12).
> BAIJ can reduce setup time (factorization) by a larger factor.
>
> Sometimes it is worth storing a small number of explicit zeros in order
> to have constant block size.  Note that many third-party preconditioners
> can not use BAIJ, but if you insert values with MatSetValuesBlock, you
> can still always run with -mat_type aij.
>
> Jed
>



-- 
Jarunan Panyasantisuk
Development Engineer
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