clear all
L=100;  delta_t=pi/L;
t = -pi : delta_t : pi; t(L+1)=1E-4
a=zeros(size(t));
for N=1:20
    D = (sin((N+1/2)*t)./sin(t/2));    
    plot(t,D,t,a),axis([-pi,pi,-10,41]),pause(1)
end