function[a,b]=rettangolo(x,y)
x=x/2;
y=y/2;
a=-x:0.01:x;
b=y;
plot(a,b,'g+');
hold on
c=-x:0.01:x;
d=-y;
plot(c,d,'g+');
e=-y:0.01:y;
f=x;
plot(f,e,'g+'),
g=-y:0.01:y;
h=-x;
plot(h,g,'g+');
axis equal