# How does Catalyst send the extracts to the ParaView server?

**URL:** https://discourse.paraview.org/t/how-does-catalyst-send-the-extracts-to-the-paraview-server/10362
**Category:** In Situ Support
**Tags:** catalyst
**Created:** [September 20, 2022, 3:57pm UTC](https://discourse.paraview.org/t/how-does-catalyst-send-the-extracts-to-the-paraview-server/10362 "2022-09-20T15:57:14Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![CsatiZoltan](https://discourse.paraview.org/user_avatar/discourse.paraview.org/csatizoltan/32/6997_2.png) [@CsatiZoltan](https://discourse.paraview.org/u/CsatiZoltan)
#### Post date: [September 20, 2022, 3:57pm UTC](https://discourse.paraview.org/t/how-does-catalyst-send-the-extracts-to-the-paraview-server/10362/1 "2022-09-20T15:57:14Z")

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I tried the [wavelet\_miniapp](https://github.com/Kitware/ParaView/blob/master/Wrapping/Python/paraview/demos/wavelet_miniapp.py) bundled with ParaView, supplying my script _sample.py_ as input to the miniapp.  
I launched the program with N being a power of two

```auto
mpiexec -np N pvbatch --sym -m paraview.demos.wavelet_miniapp --script sample.py --script-version 2 --channel Wavelet1 --timesteps 10

```

while connecting to it from the ParaView GUI.

What I noticed are the following:

1. In the Pipeline Browser, I click on the _Slice1_ object, and in the Information tab I check the bounds. It turns out that not the whole domain is shown, only N/2 part of it. Why is it so? Is the fraction 2 related to the `--sym` flag passed to _pvbatch_?
2. When I click on the icon next to _Slice1_, it sends the extract to the ParaView server (see Section 2.3 of the [Catalyst Guide](https://www.paraview.org/files/catalyst/docs/ParaViewCatalystUsersGuide_v2.pdf)). Looking at the obtained _Extract: Slice1_ object, the domain is assembled. Is it the expected behavior?
3. When I increase the number of processes, i.e. `N`, e.g. to `N=32`, the data statistics shows 0 cells for _Slice1_, but it is still assembled correctly to _Extract: Slice1_. Why is it so that afte

Performing the same co-processing on an HPC node, but with the command

```auto
mpirun -np N --npersocket N/2 $PYTHON -m paraview.demos.wavelet_miniapp --script sample.py --channel Wavelet1 --script-version 2 --timesteps 10

```

1. When I check the bounds of the domain of _Slice1_, it indicated N/2 part of the domain. But when I send it to the ParaView server by clicking on the aforementioned icon, the domain is not assembled, it stays the same. What could cause the difference compared to the previous case, when the co-processing was run on my local machine?

[sample.py](https://discourse.paraview.org/uploads/short-url/oueQmtHYVvwYZwsPxpnwdtYHGYD.py) (723 Bytes)

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<div class="post-metadata">

### Author: ![CsatiZoltan](https://discourse.paraview.org/user_avatar/discourse.paraview.org/csatizoltan/32/6997_2.png) [@CsatiZoltan](https://discourse.paraview.org/u/CsatiZoltan)
#### Post date: [October 31, 2022, 8:15am UTC](https://discourse.paraview.org/t/how-does-catalyst-send-the-extracts-to-the-paraview-server/10362/2 "2022-10-31T08:15:19Z")

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After compiling ParaView with the same C++ compiler and MPI that is used by the simulation code, all the issues above disappeared, and the coprocessing works as expected.