[petsc-users] reusing matrix created with MatCreateMPIAIJWithSplitArrays

[Dave May]

On Thursday, 30 June 2016, Hassan Raiesi <Hassan.Raiesi at aero.bombardier.com>
wrote:

> Hello,
>
>
>
> We are using PETSC in our CFD code, and  noticed that using
> “MatCreateMPIAIJWithSplitArrays” is almost 60% faster for large problem
> size (i.e DOF > 725M, using GAMG each time-step only takes 5sec, compared
> to 8.3 sec when assembling the matrix one row at a time using
> matsetvaluesblocked()  as recommended).
>
>
>
> The problem is that the memory usage goes up after each call to
> MatCreateMPIAIJWithSplitArrays  to update the matrix values.
>

Did you call MatDestroy() at each time step?

> As MatCreateMPIAIJWithSplitArrays is not supposed to copy the values, do
> we need to call it each time to update the values? We tried to just update
> the values of the diagonal and off-diagonal part of the arrays passed to
> “MatCreateMPIAIJWithSplitArrays”, (the sparsity structure is fixed) but it
> looks like that the values are not updated, what is the proper way to
> update the values of the matrix created by MatCreateMPIAIJWithSplitArrays?
>

The fool proof way would be to simply call  MatCreateMPIAIJWithSplitArrays()
and MatDestroy() at each time step (or whenever values are changed). Since
no data is actually copied, the overhead of creating the mpiaij matrix will
be minimal

Thanks,
  Dave

>
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>
> Thank you
>
>
>
> *Hassan Raiesi, *
>
> Advanced Aerodynamics Department
>
> Bombardier Aerospace
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