# Curvature (tangential divergence of normal vector)
**URL:** https://community.freefem.org/t/curvature-tangential-divergence-of-normal-vector/704
**Category:** General Discussion
**Created:** [December 24, 2020, 7:08am UTC](https://community.freefem.org/t/curvature-tangential-divergence-of-normal-vector/704 "2020-12-24T07:08:34Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Sunrise](https://community.freefem.org/u/Sunrise)
#### Post date: [December 24, 2020, 7:08am UTC](https://community.freefem.org/t/curvature-tangential-divergence-of-normal-vector/704/1 "2020-12-24T07:08:34Z")
Dear all, how to define curvature (tangential divergence of normal vector)?
Thank you in advance!
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### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [December 24, 2020, 7:36am UTC](https://community.freefem.org/t/curvature-tangential-divergence-of-normal-vector/704/2 "2020-12-24T07:36:00Z")
See [https://github.com/FreeFem/FreeFem-sources/blob/master/examples/plugin/curvature.edp](https://github.com/FreeFem/FreeFem-sources/blob/master/examples/plugin/curvature.edp).
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### Author:  [@Sunrise](https://community.freefem.org/u/Sunrise)
#### Post date: [December 26, 2020, 5:55pm UTC](https://community.freefem.org/t/curvature-tangential-divergence-of-normal-vector/704/3 "2020-12-26T17:55:36Z")
Thank you, but I get the error message
load error : Curvature
fail :
list prefix: ‘C:\Program Files\FreeFem+±cs-14.3\Contents\Windows’ ‘’ list suffix : ‘’ , ‘.dll’
Error line number 1, in file C:\Users\mmmmm\AppData\Local\Temp.ffcs6160.edp, before token Curvature
Error load
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### Author:  [@Sunrise](https://community.freefem.org/u/Sunrise)
#### Post date: [December 26, 2020, 6:01pm UTC](https://community.freefem.org/t/curvature-tangential-divergence-of-normal-vector/704/4 "2020-12-26T18:01:54Z")
Is it possible to use an extension of the form
problem Normal([nx,ny],[mx,my]) =a([nx,ny],[mx,my]) + on(1, nx=N.x,ny=N.y);
then calculate the divergence
kappa=div(nx,ny);