这个程序哪里出问题了 求大神解答

clear all; close all; clc;
x=-100:100;
y=-100:100;
z=zeros(201,201);
v=-0.5:0.002:0.5;
Q1=1;
x1=0;
y1=0;
for m=1:201
for n=1:201
z(m,n)=potential(x(n),y(m),Q1,x1,y1);
end
end
figure;
contour(y,x,z,v);