The PETSc paradigm for this is
DMView(dm, viewer); /* save mesh info
VecView(vec,viewer);
Which has basic variants
DMView(dm, viewer); /* save mesh info
VecView(vec,viewer);
VecView(vec,viewer);
...
and
VecView(vec,viewer);
...
User simply changes the viewer to select a large variety of viewers (from X
to Visit: in theory). Of course in the introductory tutorial it will be a
"simple" viewer but it is important to still have the flexible usage because
the user must learn the correct paradigm and how trivial it is to switch
viewers (in theory but not neccessarily in practice yet).
Since the vec knows about the associated DM, passing the DM separately
should be optional
1) We don't support this paradigm completely consistently/properly for all
viewers/dm combinations (we should)
2) For some combinations we have additional functionality to make it easier
to manage the relationship between the mesh and the vector
a) For example with the Matlab binary viewer and and DA it
i) saves the DA object (dof, dimensions, periodicity information,
...) as a Matlab struct so it can be easily be manipulated in
Matlab. But there is no such saving for loading into Python.
ii) saves a .info file that users can use with
PetscBinaryBinaryReadMatlab.m that automatically reshapes the vector as a
Matlab
multi-dimensional array of the appropriate shape. Nothing
similar for Python
b) for DA vectors and binary and ASCII viewers it automatically calls
DAGlobalToNatural() so the user is given the vector in the "right ordering"
c) In theory much of this could could be used for viewing from Matlab
with the Matlab engine, regular binary files, HDF matlab format files and
sockets, but the plumbing is not set up. Also python
3) What to do once the data is "in the visualizer", for example sample
python scripts, Matlab scripts, Visit directions, .... We totally lack the
directions and the scripts.
So maybe there are at least two tasks (issues?) that come with this question
I) make the paradigm more uniform and add the functionality needed to the
viewers for for more combinations.
II) add scripts and documentation for the usage.
For the beginner example I would use DMDA with
a) binary viewer for Python (plus needed utilities for reshaping
automatically like Matlab) and displaying and
b) matlab binary viewer for Matlab with script to show plotting
For DMPLEX we need something similar (same paradigm) but with some mesh
loader and etc. I would only do this for Python (and just have docs saying it
is possible for Matlab but the mesh loaders/displayers have to be written.)
Barry
A related note. For users not using a DM, the viewer defaults to a simple 1d
output of the vectors. For users of their own mesh data structure (DMSHELL)
they would be provide a viewer with DMShellSetView() (doesn't exist yet, but
should) and if they need to also manipulate the vector in the viewer they would
use VecSetOperation(VECOP_VIEW = 33, VECOP_LOAD = 41). This is an more advanced
topic.
> On Jul 25, 2019, at 11:48 AM, Jed Brown via petsc-dev <[email protected]>
> wrote:
>
> Dave May via petsc-dev <[email protected]> writes:
>
>> I'd describe how to use the binary dump and how to generate vtk files.
>>
>> The first is the most universal as it's completely generic and does not
>> depend on a dm, thus users with their own mesh data structure and or don't
>> have a mesh at all can use it. Would be worth while also providing a
>> minimal python+mathplotlib script which loads the data and spits out a PDF
>> so folks don't have to depend on matlab.
>
> If you have a parallel example that doesn't use DM, you're gonna have a
> lot of bookkeeping to plot the data after loading the vector. Seems
> like a distraction that will trap a lot of people in the minutia instead
> of the big picture.
