[petsc-users] Doubt in MPIPreallocation

[Jed Brown]

John Albequerque <johncfdcfd at gmail.com> writes:

> So Jed, what you are suggesting is that I should set only the non-zero
> elements while using
> *  MatSetValues(A,(high-low),**idxm,nc,idxn,values,INSERT_*
>
> *VALUES);*
> And not mention the zero elements and for that I should loop over all local
> rows and then set each of the value.

Yes.  The whole point of a sparse matrix is to spend no time or storage
on 0.0 entries.  If you allocate a dense matrix and store all the zeros,
you're just being inefficient relative to a dense format.
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