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
    K =1/(N+1)* (sin((N+1)/2*t)./sin(t/2)).^2;    
    plot(t,K,t,a),axis([-pi,pi,-1,20+1]),pause(1)
end