Incorrect logic in Cell definitions leading to incorrect definitions.

[jude-moo]

Bug Description

Direct reading of a geometry.xml file and immediate writing of the file is altering the geometry unintentionally.

Steps to Reproduce

for a cell defined as:

  <cell id="1" material="4" region="1 -6 (-2 -4) | (-5 3)" universe="1"/>

Run a simple python code:
geom = openmc.Geometry.from_xml('/lustre/home/jk8173/FNG_ss/openmc/write_geometry_test/geometry.2.xml')
geom.export_to_xml('geometry.out.xml')

The outputted cell is defined as,

  <cell id="1" material="4" region="(1 -6 -2 -4) | (-5 3)" universe="1"/>

Which substantially changes the geometry.

I believe the intention of the code is correct, as logically speaking these two definitions are the same. However, in OpenMC, the first line is read as:

  <cell id="1" material="4" region="1 -6 ( (-2 -4) | (-5 3) )" universe="1"/>

Environment

OpenMC version 0.15.3-dev110

Ran on Linux

geometry.2.xml

[GuySten]

However, in OpenMC, the first line is read as:

  <cell id="1" material="4" region="1 -6 ( (-2 -4) | (-5 3) )" universe="1"/>

How do you know that? Maybe it is read correctly.

[jude-moo]

@GuySten I ran the openmc-plotter for the geometry when the line was defined as:

and the geometry was the same as when the line was defined as:

[GuySten]

I could not plot your example so I prepared a simpler one:

Case 1

<?xml version='1.0' encoding='UTF-8'?>
<geometry>
  <cell id="1" material="4" region="-1 2 (-3 4) | (-5 6)" universe="1"/>
  <surface id="1" type="y-plane" coeffs="10"/>
  <surface id="2" type="y-plane" coeffs="-10"/>
  <surface id="3" type="x-plane" coeffs="10"/>
  <surface id="4" type="x-plane" coeffs="-10"/>
  <surface id="5" type="z-plane" coeffs="10"/>
  <surface id="6" type="z-plane" coeffs="-10"/>
</geometry>

Case 2

<?xml version='1.0' encoding='UTF-8'?>
<geometry>
  <cell id="1" material="4" region="-1 2 ((-3 4) | (-5 6))" universe="1"/>
  <surface id="1" type="y-plane" coeffs="10"/>
  <surface id="2" type="y-plane" coeffs="-10"/>
  <surface id="3" type="x-plane" coeffs="10"/>
  <surface id="4" type="x-plane" coeffs="-10"/>
  <surface id="5" type="z-plane" coeffs="10"/>
  <surface id="6" type="z-plane" coeffs="-10"/>
</geometry>

Case 3

<?xml version='1.0' encoding='UTF-8'?>
<geometry>
  <cell id="1" material="4" region="(-1 2 -3 4) | (-5 6)" universe="1"/>
  <surface id="1" type="y-plane" coeffs="10"/>
  <surface id="2" type="y-plane" coeffs="-10"/>
  <surface id="3" type="x-plane" coeffs="10"/>
  <surface id="4" type="x-plane" coeffs="-10"/>
  <surface id="5" type="z-plane" coeffs="10"/>
  <surface id="6" type="z-plane" coeffs="-10"/>
</geometry>

Conclusions

There is a bug in openmc. Logically case 1 and case 3 should have been the same.
In practice case 1 is wrongly interpreted as case 2.

Edit:
If I understand correctly, the bug is only when writing xml files not through the python API so it should happen only in very rare cases.