function [b,a] = f_ellipticz (F_p,F_s,delta_p,delta_s,ftype,fs,n)

%F_ELLIPTICZ: Design elliptic frequency-selective digital filter
%
% Usage: [b,a] = f_ellipticz (F_p,F_s,delta_p,delta_s,ftype,fs,n)
%
% Inputs: 
%         F_p     = passband cutoff frequency or frequencies
%         F_s     = stopband cutoff frequency or frequencies
%         delta_p = passband ripple
%         delta_s = stopband attenuation
%         ftype   = filter type
%
%                   0 = lowpass
%                   1 = highpass
%                   2 = bandpass (F_p and F_s are vectors)
%                  3 = bandstop (F_s and F_p are vectors)
%
%         fs      = sampling frequency in Hz
%         n       = an optional integer specifying the filter
%                   order.  If n is not present, an estimate of
%                   order required to meet the specifications
%                   is used.
% Outputs:  
%           b = 1 by (n+1) coefficient vector of numerator polynomial 
%           a = 1 by (n+1) coefficient vector of denominator polynomial
%
% See also: F_BUTTERZ, F_CHEBY1Z, F_CHEBY2Z

% Initialize

fs = f_clip (fs,0,fs);
F_p = f_clip (F_p,0,fs/2);
F_s = f_clip (F_s,0,fs/2);
delta_p = f_clip (delta_p,0,delta_p);
delta_s = f_clip (delta_s,0,delta_s);
ftype = f_clip (ftype,0,3);
T = 1/fs;

% Compute normalized lowpass analog filter 

switch (ftype)
case 0, r = F_p/F_s;
case 1, r = F_s/F_p;
case 2, r = max([F_s(1)/F_p(1),F_p(2)/F_s(2)]);
case 3, r = max([F_p(1)/F_s(1),F_s(2)/F_p(2)]);
end
F_0 = 1/(2*pi);
F_1 = F_0/r;
if nargin < 7
   [bs,as] = f_elliptics (F_0,F_1,delta_p,delta_s);
else
   [bs,as] = f_elliptics (F_0,F_1,delta_p,delta_s,n);
end

% Prewarp cutoff frequencies

F_p = tan(pi*F_p*T) / (pi*T);
F_s = tan(pi*F_s*T) / (pi*T);

% Convert to desired filter type

switch (ftype)
   
case 0, [B,A] = f_low2lows  (bs,as,F_p);
case 1, [B,A] = f_low2highs (bs,as,F_p);
case 2, [B,A] = f_low2bps   (bs,as,F_p(1),F_p(2));
case 3, [B,A] = f_low2bss   (bs,as,F_p(1),F_p(2));
   
end

% Convert to digital filter

[b,a] = f_bilin  (B,A,fs);