On Tue, 17 Nov 2015, Miguel Angel Salazar de Troya wrote:

> What's the difference between .xda and .xdr?

ASCII vs (platform-independent) binary.  xdr files are smaller (unless
you use xda.gz or xda.bz2), xda files are easier to debug.  I like
using xda.gz myself; bz2 conversions aren't done in-stream and are
costly; xdr works great 99% of the time, right up until you have a bug
so confusing that you want to look at restart files directly.

> Last time I pulled libmesh was a couple months ago.

That should have been sufficient;
https://github.com/libMesh/libmesh/pull/618 was merged on Aug 7.

> I'm going to fetch and try again. Before that, leaving just
> EquationSystems::READ_DATA and write and reading the file as
> "eq_output.xda" in the argument still gives me the same error.

Hmm... I wonder if you've got the application init-then-read bug that
we test for as of https://github.com/libMesh/libmesh/pull/689 last
month?

> I've also realized that EquationSystems::write() doesn't record the
> mesh information, does it?

No.  If you don't modify the mesh in between restarts then you don't
want to bother writing out redundant copies of it.

> That means we should be careful the mesh matches the mesh we called
> EquationSystems::write() with.

Definitely!  This could also manifest as the bug you reported.

> Is there anyway to load all this information?

mesh.write("my_mesh.xda.gz");
es.write("my_soln.xda.gz", WRITE_DATA | WRITE_ADDITIONAL_DATA);

> For instance, I can record all this information with an ExodusII_IO
> object for plotting purposes. Can I load it and use it in my mesh
> and EquationSystems?

Not safely in general.  ExodusII doesn't store the mesh hierarchy, it
"flattens" the mesh by only outputting active elements.  Try to read
that in again and you get a torn mesh at hanging nodes; add a solution
on top and you get scrambled garbage.

If you're not using any adaptivity or non-lagrange FEs, then I believe
we support reading meshes and solutions (via some API in ExodusII_IO,
I think?  I don't use this myself) from ExodusII.
---
Roy

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