# My CMFD isn't working properly

**URL:** <https://openmc.discourse.group/t/my-cmfd-isnt-working-properly/5573>\
**Category:** User Support\
**Created:** [June 6, 2025, 5:17am UTC](https://openmc.discourse.group/t/my-cmfd-isnt-working-properly/5573 "2025-06-06T05:17:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![s\_rahman\_wave](https://avatars.discourse-cdn.com/v4/letter/s/b5ac83/32.png) [@s\_rahman\_wave](https://openmc.discourse.group/u/s_rahman_wave)\
**Post date:** [June 6, 2025, 5:17am UTC](https://openmc.discourse.group/t/my-cmfd-isnt-working-properly/5573/1 "2025-06-06T05:17:07Z")

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I was calculating adjoint neutron flux by CMFD approach. Now it’s coming up with error that I can’t solve .Can anyone say what’s the problem here?

 ![Screenshot 2025-06-05 at 12.55.26 AM](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/f/f5422e6f2f55fd77d16c81b2ad435e71840f0e42.png)  
 ![Screenshot 2025-06-05 at 10.16.02 PM](https://global.discourse-cdn.com/free1/uploads/openmc/original/2X/3/30babc16d7af7d0fad0456702ef643316b71283d.png)

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**Author:** ![tjlaboss](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/tjlaboss/32/1390_2.png) [@tjlaboss](https://openmc.discourse.group/u/tjlaboss)\
**Post date:** [June 6, 2025, 8:21pm UTC](https://openmc.discourse.group/t/my-cmfd-isnt-working-properly/5573/2 "2025-06-06T20:21:57Z")

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If your model is otherwise valid, then most likely, you have have mesh cells in your CMFD calculation outside where they should be. You might see this if you have misconfigured your mesh bounds, or if you have a non-rectangular geometry. You may find it useful to review [CMFDMesh.map](https://docs.openmc.org/en/stable/pythonapi/generated/openmc.cmfd.CMFDMesh.html).

P.S. It better to include code snippets, rather than screenshots of text. Use triple backticks to insert a code block. E.g., for a Python snippet,

` ```python`  
`<your code here>`  
`````