[petsc-dev] Checkpoint-restart with DMPlex objects

[Jed Brown]

Hapla Vaclav via petsc-dev <petsc-dev at mcs.anl.gov> writes:

> So my overall idea (which I presented also at this year's User Meeting
> in London and nobody has objected yet), is that some FE codes could
> potentially use only this for both checkpointing and
> viewing. Advantages would include removing the redundancy in storage
> (reducing the file size) and increased interoperability with 3rd party
> tools.

This is great in principle, but note that visualization files often
contain diagnostic quantities like pressure, temperature, and vorticity
while checkpoint files contain only state variables like density,
momentum, and total energy.  Although one can be derived from the other,
it requires an equation of state (an arbitrarily complex constitutive
model) and/or compatible derivatives, both of which are so cumbersome to
provide to offline visualization that almost nobody has an appetite for
it.

It certainly makes sense to use the same format that can include
arbitrary diagnostic quantities.  I think that should be provided by an
extensible Viewer filter so the caller (e.g., a TS monitor) can just
call VecView and the viewer's configuration determines which diagnostic
and/or state quantities to include.

Note that Vec holds a reference to its DM so it can determine whether
the topology is already present in the output file and link itself
appropriately.  There should be no assumption that there is only one DM
or that it has already been written.