dfdzeta.m

AFD - Advanced Filter Design using MATLABMiroslav D. Lutovac, Dejan V. Tosicversion 1.00 released 15

function z = dfdzeta(n, a, e)

% dfdzeta.m  DFD zeta(n,a,e)
%
%   Authors: Dejan V. Tosic, Miroslav D. Lutovac, 1999.03.08
%                 [e-mail]
%                 [e-mail]
%
%   Copyright (c) 1999 by Tosic & Lutovac
%   $Revision: 1.0 $  $Date: 1999/03/08 03:07:42 $
%
%   References:
%        Miroslav D. Lutovac, Dejan V. Tosic, Brian L. Evans
%           Advanced Filter Design for Signal Processing
%                   Using MATLAB and Mathematica

%  calls:
%% dfdl.m, dfdv.m

if e >= 0.000000002
 L = dfdl(n,a);
 mL = (L^2-1)/L^2;
 ma = (a^2-1)/a^2;
 
 KL = ellipke(1/L^2);
 Ka = ellipke(1/a^2);

 global ELLIP_ML ELLIP_EPSILON;
 ELLIP_ML = mL;
 ELLIP_EPSILON = e;
 
 v0 = log((sqrt(1+e^2)+1))-log(e);   %v0 = atanh(1/sqrt(1+e^2));
 v = fmins('dfdv', v0);
 z = abs(ellipj(v*Ka/(n*KL),ma));
else
 z = 1;
end