[petsc-users] DMPlex and HDF5 vector ordering

[Matthew Knepley]

On Fri, May 8, 2015 at 1:48 AM, Justin Chang <jychang48 at gmail.com> wrote:

> I also had the same issue. My current work around is the following.
>
> 1) Run the first DMPlex program on one process and write the vector into
> HDF5.
>
> 2) Run the second DMPlex program with any number of processes but do the
> following:
>
> 3) After you create the initial DMPlex on rank 0, but before distributing
> it, duplicate it and create its petscsection and vector.
>
> 4) Load the HDF5 file into that vector. At this point the ordering is the
> same.
>
> 5) Distribute the original DM and save the PetscSF.
>
> 6) Call DMPlexDistributeField() to distribute the vector.
>
>
> This will guarantee the right ordering for the second program no matter
> how many processes it uses. Only drawback is that the first program has to
> be run in serial. I am also looking for a better way. Matt any thoughts?
>

Ata and Blaise have a pull request coming that creates a "natural ordering"
for a Plex, similar to the
one used by DMDA, so you get output that is invariant to process number. It
may take until the end
of the summer to get it fully integrated, but it is very close.

  Thanks,

     Matt


> Thanks,
> Justin
>
>
> On Friday, May 8, 2015, Adrian Croucher <a.croucher at auckland.ac.nz> wrote:
>
>> hi,
>>
>> I create a Vec on a DMPlex using DMPlexCreateGlobalVec(), then write it
>> to HDF5 using PetscViewerHDF5Open() and VecView().
>>
>> I then try to read it back in later (in another program, but using the
>> same DMPlex) using PetscViewerHDF5Open() and VecLoad().
>>
>> It looks like the ordering of the final vector entries in the second
>> program depends on how many processors I use. If they are the same in both
>> programs, I get the right ordering, but if they aren't, I don't. Is that
>> expected? If so, is there any way to guarantee the right ordering when I
>> read the Vec back in?
>>
>> - Adrian
>>
>> --
>> Dr Adrian Croucher
>> Senior Research Fellow
>> Department of Engineering Science
>> University of Auckland, New Zealand
>> email: a.croucher at auckland.ac.nz
>> tel: +64 (0)9 923 84611
>>
>>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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