matlab error Hdiv, L2, H1

Hello,

I have my exact solution $u$ and calculated by the mixed finite element method $u_h$ , and I wonder if given such data and mesh data can help me:

script.m find a matlab command or allow me to calculate the errors, ie the norm of the difference between the exact solution and the approximation using finite element method (mixed) (norm $L ^ 2(\Omega)$ , $H ^ 1(\Omega)$ and $H (div;\Omega)$ ).

Thanks,

any help or references are welcome.http://www.google.com/images/cleardot.gif