/usr/share/octave/packages/signal-1.3.2/ellip.m is in octave-signal 1.3.2-1+b1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 | ## Copyright (C) 2001 Paulo Neis <p_neis@yahoo.com.br>
## Copyright (C) 2003 Doug Stewart <dastew@sympatico.ca>
##
## This program is free software; you can redistribute it and/or modify it under
## the terms of the GNU General Public License as published by the Free Software
## Foundation; either version 3 of the License, or (at your option) any later
## version.
##
## This program is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public License along with
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {[@var{b}, @var{a}] =} ellip (@var{n}, @var{rp}, @var{rs}, @var{wp})
## @deftypefnx {Function File} {[@var{b}, @var{a}] =} ellip (@var{n}, @var{rp}, @var{rs}, @var{wp}, "high")
## @deftypefnx {Function File} {[@var{b}, @var{a}] =} ellip (@var{n}, @var{rp}, @var{rs}, @var{[wl}, @var{wh}])
## @deftypefnx {Function File} {[@var{b}, @var{a}] =} ellip (@var{n}, @var{rp}, @var{rs}, @var{[wl}, @var{wh}], "stop")
## @deftypefnx {Function File} {[@var{z}, @var{p}, @var{g}] =} ellip (@dots{})
## @deftypefnx {Function File} {[@var{a}, @var{b}, @var{c}, @var{d}] =} ellip (@dots{})
## @deftypefnx {Function File} {[@dots{}] =} ellip (@dots{}, "s")
##
## Generate an elliptic or Cauer filter with @var{rp} dB of passband ripple and
## @var{rs} dB of stopband attenuation.
##
## [b,a] = ellip(n, Rp, Rs, Wp)
## low pass filter with order n, cutoff pi*Wp radians, Rp decibels
## of ripple in the passband and a stopband Rs decibels down.
##
## [b,a] = ellip(n, Rp, Rs, Wp, 'high')
## high pass filter with cutoff pi*Wp...
##
## [b,a] = ellip(n, Rp, Rs, [Wl, Wh])
## band pass filter with band pass edges pi*Wl and pi*Wh ...
##
## [b,a] = ellip(n, Rp, Rs, [Wl, Wh], 'stop')
## band reject filter with edges pi*Wl and pi*Wh, ...
##
## [z,p,g] = ellip(...)
## return filter as zero-pole-gain.
##
## [...] = ellip(...,'s')
## return a Laplace space filter, W can be larger than 1.
##
## [a,b,c,d] = ellip(...)
## return state-space matrices
##
## References:
##
## - Oppenheim, Alan V., Discrete Time Signal Processing, Hardcover, 1999.
## - Parente Ribeiro, E., Notas de aula da disciplina TE498 - Processamento
## Digital de Sinais, UFPR, 2001/2002.
## - Kienzle, Paul, functions from Octave-Forge, 1999 (http://octave.sf.net).
## @end deftypefn
function [a, b, c, d] = ellip (n, rp, rs, w, varargin)
if (nargin > 6 || nargin < 4 || nargout > 4 || nargout < 2)
print_usage ();
endif
## interpret the input parameters
if (! (isscalar (n) && (n == fix (n)) && (n > 0)))
error ("ellip: filter order N must be a positive integer");
endif
stop = false;
digital = true;
for i = 1:numel (varargin)
switch (varargin{i})
case "s"
digital = false;
case "z"
digital = true;
case {"high", "stop"}
stop = true;
case {"low", "pass"}
stop = false;
otherwise
error ("ellip: expected [high|stop] or [s|z]");
endswitch
endfor
if (! ((numel (w) <= 2) && (rows (w) == 1 || columns (w) == 1)))
error ("ellip: frequency must be given as WC or [WL, WH]");
elseif ((numel (w) == 2) && (w(2) <= w(1)))
error ("ellip: W(1) must be less than W(2)");
endif
if (digital && ! all ((w >= 0) & (w <= 1)))
error ("ellip: all elements of W must be in the range [0,1]");
elseif (! digital && ! all (w >= 0))
error ("ellip: all elements of W must be in the range [0,inf]");
endif
if (! (isscalar (rp) && isnumeric (rp) && (rp >= 0)))
error ("ellip: passband ripple RP must be a non-negative scalar");
endif
if (! (isscalar (rs) && isnumeric (rs) && (rs >= 0)))
error ("ellip: stopband attenuation RS must be a non-negative scalar");
endif
## Prewarp the digital frequencies
if (digital)
T = 2; # sampling frequency of 2 Hz
w = 2 / T * tan (pi * w / T);
endif
## Generate s-plane poles, zeros and gain
[zero, pole, gain] = ncauer (rp, rs, n);
## splane frequency transform
[zero, pole, gain] = sftrans (zero, pole, gain, w, stop);
## Use bilinear transform to convert poles to the z plane
if (digital)
[zero, pole, gain] = bilinear (zero, pole, gain, T);
endif
## convert to the correct output form
if (nargout == 2)
a = real (gain * poly (zero));
b = real (poly (pole));
elseif (nargout == 3)
a = zero;
b = pole;
c = gain;
else
## output ss results
[a, b, c, d] = zp2ss (zero, pole, gain);
endif
endfunction
%!demo
%! [n, Ws] = ellipord ([.1 .2], [.01 .4], 1, 90);
%! [b, a] = ellip (5, 1, 90, [.1 .2]);
%! [h, w] = freqz (b, a);
%!
%! plot (w./pi, 20*log10 (abs (h)), ";;")
%! xlabel ("Frequency");
%! ylabel ("abs(H[w])[dB]");
%! axis ([0, 1, -100, 0]);
%!
%! hold ("on");
%! x=ones (1, length (h));
%! plot (w./pi, x.*-1, ";-1 dB;")
%! plot (w./pi, x.*-90, ";-90 dB;")
%! hold ("off");
%% Test input validation
%!error [a, b] = ellip ()
%!error [a, b] = ellip (1)
%!error [a, b] = ellip (1, 2)
%!error [a, b] = ellip (1, 2, 3)
%!error [a, b] = ellip (1, 2, 3, 4, 5, 6, 7)
%!error [a, b] = ellip (.5, 2, 40, .2)
%!error [a, b] = ellip (3, 2, 40, .2, "invalid")
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