// Min Plot
t= -%pi:0.05:%pi;
// the last `;' silences the command; %pi is pi; t does steps of 0.05 from
// -pi to +pi
f= sign(t);
// f(x) is the function that is 1 0<x<pi and -1 -pi<x<0
plot(t,f,"b") // plot the function in blue
plot(t,(4/%pi)*(sin(t)+sin(3*t)/3+sin(5*t)/5),"r") // plot the approx in red
// in the graphics click on the file menu select print 
// or save to postscript file
xs2eps(0,'foo.eps')