# Asertion fail for multi-cores

**URL:** <https://community.freefem.org/t/asertion-fail-for-multi-cores/1245>\
**Category:** General Discussion\
**Created:** [October 4, 2021, 4:15pm UTC](https://community.freefem.org/t/asertion-fail-for-multi-cores/1245 "2021-10-04T16:15:28Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![yongxing](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/yongxing/32/3632_2.png) [@yongxing](https://community.freefem.org/u/yongxing)\
**Post date:** [October 4, 2021, 4:15pm UTC](https://community.freefem.org/t/asertion-fail-for-multi-cores/1245/1 "2021-10-04T16:15:28Z")

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After reading an external mesh file, I got the following assertion fail when using 4 CUPs, but there is no such an error if I use 1 CUP. What’s the problem?

![image](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/1X/0131abecba90dcd96f6a5b3401f29c4a86fde20d.png)

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**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [October 4, 2021, 4:50pm UTC](https://community.freefem.org/t/asertion-fail-for-multi-cores/1245/2 "2021-10-04T16:50:41Z")

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There is something wrong with your mesh. Using a single process, just do `mesh3 bug = trunc(Th, 1);` and you’ll see the same assertion failure.