flux line

hi , I have this program for calculate the V(x,y) and I want to sketch of flux lines and equipotential lines using matlab. By given : For b = a=0.25m , (V0)=50 V we have V(x,y)=(-4(V0)/pi) sum(sin((n*pi*x)/b)*sinh((n*pi*(a-y))/b))/(n*sinh(n*pi*a)/b))

"% SOLUTION OF LAPLACE'S EQUATION

%======================

% THIS PROGRAM SOLVES THE TWO-DIMENSIONAL

% BOUNDARY-VALUE PROBLEM

% a AND b ARE THE DIMENSIONS OF THE TROUGH

% x AND y ARE THE COORDINATES OF THE POINT % OF INTEREST

P = [ ] ;

Vo = 100.0;

a = 1.0;

b = a;

x = b/4;

y= 3.*a/4.;

c = - 4.*Vo/pi

sum = 0.0;

for k=l:10

n = 2*k - 1

al = sin(n*pi*x/b);

a2 = sinh(n*pi*(a-y)/b);

a3 = n*sinh(n*pi*a/b);

sum =sum + c*al*a2/a3;

P = [n, sum]

end

diary test.out

P

diary off "

Can you help me????