i=1:0.01:pi;
x=1:0.01:pi;
N1=13;
N2=15;
for i=1:pi+1
if 0.4*pi+1<=x(i)+1 && x(i)+1<=0.6*pi+1
phi_2(i)=(N2-N1)*x(i)+1/2;
end
if 0.0*pi+1<=x(i)+1 && x(i)+1<=0.2*pi+1
phi_2(i)=((N2-N1)*x(i)+1+pi)*0.5;
end
end
syms i;
Er=1-abs(exp(1j*(phi_2(i)-((N1+N2)/2)*i)).*cos(((N2-N1)/2)*i-phi_2(i) )).^2;
s=int((Er),0.4*pi,0.6*pi);