This is the code from the file midterm3.m

This code is used to graph phi, parts of the equation for phi and the laplacian of 
phi and the parts of phi.

x=0.00001:.01:.5;  
y=0.00001:.01:.5;  
[xx,yy]=meshgrid(x,y);  

a0 = 1;  
q = 1;  
a = 2/a0;  

coord = (xx-0).^2+(yy-0).^2;  
r = sqrt(coord);  

phi = q * exp((-a).*r) ./ r .*(1.+a.*r./2);  

phi1 = q * exp((-a).*r) ./ r;  

phi2 = q * exp((-a).*r) ./ r .* a .* r./ 2;  

lp = del2(phi);  

mesh(lp)