%例程4－12   Ⅲ、Ⅳ型理想低通濾波器的單位沖激響應 計算

function hd=ideal_lp2(Wc,N)
%compute the ideal lowpass fiter unit pulse respondence hd(n)
%wc: cutoff frequency
%N: window length
%hd: unit pulse respondence

alpha=(N-1)/2;
n=0:1:N-1;
m=n-alpha+eps;
hd=cos(Wc*m)./(pi*m);