[petsc-users] MatMPIAIJSetPreallocation question

[Xiangdong]

Hi Barry,

Thanks for your response. So these extra allocated memory is just a waste
of memory, but no harm for other mat related computation. Is it correct?

Thank you.

Xiangdong

On Fri, Aug 4, 2017 at 4:52 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Aug 4, 2017, at 2:52 PM, Xiangdong <epscodes at gmail.com> wrote:
> >
> > Hello everyone,
> >
> > I have a quick questions on the MatMPIAIJSetPreallocation. If we do not
> pass the exact number of nonzeros for o_nnz and d_nnz, (for example,
> MAT_INFO_NZ_ALLOCATED is 50% more than MAT_INFO_NZ_USED), will the
> performance of MatMult be affected? What effect will these allocated but
> unused memory cause?
>
>    It is not a big deal to have extra memory, it won't slow things down.
> If you under estimate it can slow things down a lot.
>
> >
> > Thank you.
> >
> > Best,
> > Xiangdong
>
>
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