Curvature (tangential divergence of normal vector)

Dear all, how to define curvature (tangential divergence of normal vector)?
Thank you in advance!


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

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