how to calculate the potential of a uniformly charged plate, using the trapezoidal method

I am trying to create a program that calculates the potential in several points out of a plate loaded uniformly with a function of density f (x, y) with the method of the trapeze. But I have problems on having calculated and to obtain the information, since and created cycles in order that each of the points cross me in the plate or out of her to form the vector direction necessarily for the calculation, but one creates several counterfoils with different values for every point out of the plate,plotting the final matrix obtained. But I need the only counterfoil for graph with the values of all the points