function [Hr,w,a,L] = hr_type1(h);
% 計算所設計的I型濾波器的振幅響應
% Hr = 振幅響應
% a = I型濾波器的系數
% L = Hr的階次
% h = I型濾波器的單位沖激響應

M = length(h);
L = (M-1)/2;
a = [h(L+1) 2*h(L:-1:1)];
n = [0:1:L];
w = [0:1:500]'*2*pi/500;
Hr = cos(w*n)*a';