Hi Subway,
for vector-valued functions you can compute the Jacobian matrix and then choose the j-th partial derivative of the i-th component of the vector. E.g.:
Code:
fes = HCurl(mesh, order=2)
u,v = fes.TnT()
a = BilinearForm(fes)
a += Grad(u)[0,1]*Grad(v)[0,1]*dx #dx_2u_1*dx_2v_1
Using Grad gives always the Jacobian, grad gives, depending on the finite element space, the Jacobian or the transpose of the Jacobian.
Best,
Michael