Variable coefficient in LHS

Hi,
         I'm pretty new to Fenics, so the solution to my question may be obvious, but I'm still struggling to crack on it. Basically, I have a Coefficient in the LHS of my variational equation that varies along the Grid nodes:

# Equation
a = ((k**2 / n**2) * inner(E, v) - inner(nabla_grad(E), nabla_grad(v))) * dx

That's the 'k' coefficient and it different values. I have all these values stored in a matrix of the same order as the Mesh grid (100x100 grid and a 100x100 matrix with all the k values).

Is there a simple way to make the solver take account of such spatial variable coefficient values?

Thanks in advance,
Patricio,