function y=IIR(fai,M)
w=0:pi/(M-1):pi;
z1=exp(-j.*w);z2=z1.*z1;
y=ones(1,M);
k=10;
for n1=1:k
    m1=4*(n1-1);
    x(n1)=abs((1+fai(m1+1)*z1+fai(m1+2)*z2)/(1+fai(m1+3)*z1+fai(m1+4)*z2));
    y=y*x(n1);
end