function test
clc
x0=500;y0=100;x1=520;a=0.2;b=0.1;n=10;

[x,y]=spiderFun(x0,y0,x1,a,b,n);
plot(x); grid;

hold on;
plot(y); grid;

function [x,y]=spiderFun(x0,y0,x1,a,b,n)
x(1)=x0;y(1)=y0;x(2)=x1;
for k=2:n-1
y(k)=y(k-1)-b*x(k);
x(k+1)=x(k)+a*y(k);
end
y(n)=y(n-1)-b*x(n);