a=1;
w=1;
t= -2*pi:0.1:2*pi;
y = A/2 + 2*A/pi*(cos(t)-1/3*cos(3*t) + 1/5* cos(5*t) - 1/7 * cos(7*t) + 1/9*cos(9*t) - 1/11*cos(11*t));
plot(t,y);