# How to define curvature on the boundary

**URL:** <https://community.freefem.org/t/how-to-define-curvature-on-the-boundary/3504>\
**Category:** General Discussion\
**Created:** [September 20, 2024, 1:48pm UTC](https://community.freefem.org/t/how-to-define-curvature-on-the-boundary/3504 "2024-09-20T13:48:13Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![amirayh](https://avatars.discourse-cdn.com/v4/letter/a/8dc957/32.png) [@amirayh](https://community.freefem.org/u/amirayh)\
**Post date:** [September 20, 2024, 1:48pm UTC](https://community.freefem.org/t/how-to-define-curvature-on-the-boundary/3504/1 "2024-09-20T13:48:13Z")

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Hello,  
I have the following code in FreeFEM to compute the curvature on the boundary:  
Vh H = curvature(Th, 2);  
I know that `H = div(n)` where `n` is the normal of the boundary. However, I would like to better understand how this curvature is being computed and how exactly the normal vector `n` is defined in this context.  
Could someone please explain how the curvature is calculated and how the normal is determined in FreeFEM?