How to calculate nodal velocity for 2D domian from the calculated Pressure head

Hi,

I have suceeed in making a code for water flow in unsaturated  media by using FAESOR, I am having a trouble in calculating the velocity from this nodal pressure in x and z direction. Flux equation is  Q =  K(nabla) (Ψ+1).. (I did not find the symbole for nabla in your symbols for writing the BODY).

For this I use  Flux = ((Ns{j})'*((HYC* (Jac * w(j)))*Ndersp')')',,, where HYC is the similar to Hydraulic conductivity similar to heat conductivity.

Above formula gives me Flux, a array having two elements, 

First of all is this correct formulation for deriving  K(nabla). which can be multiplied by Ψ  in mail script to find the flux. ????

if it is correct ??? how to assemble each of the element from this array in Gobal matrix. 

Thanks

Shirish