# Problem with peridicity " Periodic: the both number of edges is not the same"

**URL:** <https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914>\
**Category:** General Discussion\
**Created:** [May 13, 2025, 8:59am UTC](https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914 "2025-05-13T08:59:21Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![taha](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@taha](https://community.freefem.org/u/taha)\
**Post date:** [May 13, 2025, 8:59am UTC](https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914/1 "2025-05-13T08:59:22Z")

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[diffusion-convection.edp](https://community.freefem.org/uploads/short-url/2aH8u8W6ZVEbf0tOXERs7NhO7pI.edp) (3.8 KB)  
Hello everyone,i hove you are doing well,i’m solving a convection-diffution problem in solid/fluid but i’m trying to do a periodicity but it gave me this error " Periodic: the both number of edges is not the same" however i used the same mesh density for all borders and used fixborder=true,and thank you so much for your help

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**Author:** ![fb77](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/fb77/32/3796_2.png) [@fb77](https://community.freefem.org/u/fb77)\
**Post date:** [May 13, 2025, 3:33pm UTC](https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914/2 "2025-05-13T15:33:28Z")

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Hello Taha,  
Your labels 9 and 11 are not set to the correct boundaries, indeed your “bottom” and “top” borders for solid3 and solid4 are inverted.  
Moreover you did not give labels to some borders. In this situation freefem automatically gives some labels, and they can be identical to some of your labels. It then gives an error when you associate the corresponding label in periodic boundaries.  
The solution is simple: give a label to all the boundaries.

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**Author:** ![taha](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@taha](https://community.freefem.org/u/taha)\
**Post date:** [May 13, 2025, 3:38pm UTC](https://community.freefem.org/t/problem-with-peridicity-periodic-the-both-number-of-edges-is-not-the-same/3914/3 "2025-05-13T15:38:46Z")

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Hello François,  
It did work fine,thank you so mush !!