Rate of change in temperature at everypoint on a heated circle

General Discussion
7

You can compute it yourself using the known geometry of your mesh. Or you can do something like:

varf vHF(p,q) = on(BoundaryLabel, p = N.x*dx(T) + N.y*dy(T));
Vh HF;
HF[] = vHF(0,Vh,tgv=1);