function [Hr,w,d,L] = hr_type4(h);
% 計算所設計的IV型濾波器的振幅響應
% Hr = 振幅響應
% d = IV型濾波器的系數
% L = Hr的階次
% h = IV型濾波器的單位沖激響應

M = length(h);
L = M/2;
d = 2*[h(L:-1:1)];
n = [1:1:L];
n=n-0.5;
w = [0:1:500]'*2*pi/500;
Hr = sin(w*n)*d';