[petsc-dev] DMplex: Natural Ordering and subDM

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:

> On Mon, Nov 27, 2017 at 9:24 PM, Jed Brown <jed at jedbrown.org> wrote:
>
>> Matthew Knepley <knepley at gmail.com> writes:
>>
>> > On Mon, Nov 27, 2017 at 8:08 PM, Jed Brown <jed at jedbrown.org> wrote:
>> >
>> >> I don't know the answer to your question (Matt?), but do you really need
>> >> to reorder the entire mesh or would it be sufficient to label your
>> >> points with their original numbering?
>> >
>> >
>> > Maybe I am wrong, but I think it amounts to the same thing. If we are
>> going
>> > to output things in parallel,
>> > we would need to communicate to he writing process, which this
>> essentially
>> > does.
>>
>> Writing a label doesn't require redistribution of the mesh.  It's possible
>> to do parallel IO.
>>
>
> My understanding is that 3rd party programs want the mesh in the
> original order, so we want it ordered in the HDF5 file in the original
> order. You could I guess write it in the order, but it seems messy to
> write stuff all over the place in the file. Is that what you mean?

What is the third-party program doing?  It might be easier for it to
apply the permutation than for PETSc to redistribute in order to write
the file in a possibly poor ordering.