[petsc-users] scaling a parallel matrix

[Jed Brown]

On Fri, Sep 23, 2011 at 13:35, khalid ashraf <khalid_eee at yahoo.com> wrote:

> Hi, I have a vector defined on a 3D DA of size ~1000X1000X30. I run the
> program on ~4000 processors.
> After doing the calculations, print the vector in vtk format. I need to
> print about ~10 times at different time steps.
> The printing takes about 3 hours. Is there a way to reduce the time
> required to print parallel vector printing.
>

The VTK ASCII format is a horrible parallel format. One reliable option if
you like the VTK tool chain is to write a "parallel" VTK XML format with
binary appended data. You can also write an HDF5 file and either provide
your own reader for whatever visualization software you are using or write
an XDMF file to inform the reader of what to find where.


>
> I am trying to average over some blocks of grid points and represent the
> data with a smaller sized vector defined on a smaller 3D DA. One thing I am
> not clear is that how to get the same layout for the large and smaller DA,
> so that all the calculations are local when doing the averaging. Could you
> please provide any guidance ?
>

See the lx,ly,lz parameters to DMDACreate3d().

http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-dev/docs/manualpages/DM/DMDACreate3d.html
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