low_mul_ma_ph.m

信号处理－滤波器设计（基于matlab和Mathmatica的设计方法）中关于无乘法器椭圆IIR滤波器设计的原创程序。

function [num,den]=low_Mul_Ma_Ph(n,a,Bi)
% low_Mul_bodemag.m 计算幅频响应和相频响应，并绘制
%  $date 3/12/2005
%
%   作者：赵泽平
%      [e-mail]
%   
%
%   References:
%        Miroslav D. Lutovac, Dejan V. Tosic, Brian L. Evans
%           Advanced Filter Design for Signal Processing
%                   Using MATLAB and Mathematica
z=tf('z');
numi=cell(1,(n+1)/2);
deni=cell(1,(n+1)/2);
%生成各式对应的分子分母
numi{1,1}=[Bi(1),1];
deni{1,1}=[1,Bi(1)];
for i=2:(n+1)/2
    numi{1,i}=[Bi(i),a*(1+Bi(i)),1];
    deni{1,i}=[1,a*(1+Bi(i)),Bi(i)];
end
Hi=tf(numi,deni,'variable','z')
Ha=Hi(1);
for i=2:fix((n+3)/4)
    Ha=Ha*Hi(i);
end
Hb=1;
for i=fix((n+7)/4):(n+1)/2
    Hb=Hb*Hi(i);
end
display('总的表达式为：')
H=(Ha+Hb)/2
%绘制幅频相频响应
[numH,denH] = tfdata(H);
num=numH{1,1};
den=denH{1,1};
figure
f=0:0.0001:0.5;
w=2*pi*f;
freqz(num,den,w);