low_mu_dx.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 Low_Mu_dX(n,a,Bi,serial_num,Fs)
%  Low_Mu_dX.m  绘制d/dX图
%  $date 8/10/2005
%
%   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
figure;
string_array={1:n};
f=0:0.001:0.5;
Q=sin(2*pi*f)./(1+Bi(1)^2+2*Bi(1)*cos(2*pi*f));
plot(f,Q,'LineWidth',2.5);hold on
string=sprintf('α1');
string_array{1}=string;
colormap=colorcube(n-1);
k=2;
for i=2:1:(n+1)/2
    if i<=fix((n+3)/4);
        j=1/2;
    else
        j=-1/2;
    end
    Q=j*2*(1-Bi(i)^2)*sin(2*pi*f)./...
    ((1-Bi(i))^2+a^2*(1+Bi(i))^2+2*a*(1+Bi(i))^2*cos(2*pi*f)+4*Bi(i)*(cos(2*pi*f)).^2);
    plot(f,Q,'color',colormap(3*i-5:3*i-3));hold on
    string=sprintf('α%d',i);
    string_array{k}=string;
    k=k+1;
    Q=j*4*(a+cos(2*pi*f)).*sin(2*pi*f)./...
    ((1-Bi(i))^2+4*Bi(i)*(cos(2*pi*f)).^2+a*(1+Bi(i))^2*(a+2*cos(2*pi*f)));
    if i==serial_num
        plot(f,Q,'color',colormap( 3*i-5+3*(n-1)/2 : 3*i-3+3*(n-1)/2 ));
        hold on
    else
        plot(f,Q,'color',colormap( 3*i-5+3*(n-1)/2 : 3*i-3+3*(n-1)/2 ),'LineWidth',2.5);
        hold on
    end
    string=sprintf('β%d',i);
    string_array{k}=string;
    k=k+1;    
end
legend(string_array);
xlabel('f');
ylabel('d\phi/dX');

t=0:0.001:0.5;
ax=axis;
ft(1:Fs/0.001+1)=ax(3);
ft(Fs/0.001+2:0.5/0.001+1)=ax(4)/2;
plot(t,ft,'--r')
hold off