% Chapter 8: Example 8.24%            Elliptic Lowpass Filter Design:%                Use of the ELLIP function%% Digital Filter Specifications:wp = 0.2*pi;                         %digital Passband freq in Hzws = 0.3*pi;                         %digital Stopband freq in HzRp = 1;                              %Passband ripple in dBAs = 15;                             %Stopband attenuation in dB% Analog Prototype Specifications:T = 1;                               %Set T=1OmegaP = (2/T)*tan(wp/2);            %Prewarp Prototype Passband freqOmegaS = (2/T)*tan(ws/2);            %Prewarp Prototype Stopband freqep = sqrt(10^(Rp/10)-1);             % Passband Ripple parameterRipple = sqrt(1/(1+ep*ep));          % Passband RippleAttn = 1/(10^(As/20));               % Stopband Attenuation% Analog Elliptic Filter order calculations:ep = sqrt(10^(Rp/10)-1);             %Passband Ripple FactorA = 10^(As/20);                      %Stopband Attenuation FactorOmegaC = OmegaP;                     %Analog Prototype Cutoff freqk = OmegaP/OmegaS;                   %Analog Prototype Transition Ratio;k1 = ep/sqrt(A*A-1);                 %Analog Prototype Intermediate cal.capk = ellipke([k.^2 1-k.^2]);capk1 = ellipke([(k1 .^2) 1-(k1 .^2)]);N = ceil(capk(1)*capk1(2)/(capk(2)*capk1(1)));fprintf('\n*** Elliptic Filter Order = %2.0f \n',N)%%*** Elliptic Filter Order =  3 % Digital Elliptic Filter Design:wn = wp/pi;                          %Digital Passband freq in pi units[b,a]=ellip(N,Rp,As,wn);[b0,B,A] = dir2cas(b,a)%%b0 = 0.1214%%B = 1.0000   -1.4211    1.0000%%    1.0000    1.0000         0%%A = 1.0000   -1.4928    0.8612%%    1.0000   -0.6183         0