/usr/share/octave/packages/signal-1.3.2/besself.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 | ## Copyright (C) 1999 Paul Kienzle <pkienzle@users.sf.net>
## Copyright (C) 2003 Doug Stewart <dastew@sympatico.ca>
## Copyright (C) 2009 Thomas Sailer <t.sailer@alumni.ethz.ch>
##
## 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}] =} besself (@var{n}, @var{w})
## @deftypefnx {Function File} {[@var{b}, @var{a}] =} besself (@var{n}, @var{w}, "high")
## @deftypefnx {Function File} {[@var{z}, @var{p}, @var{g}] =} besself (@dots{})
## @deftypefnx {Function File} {[@var{a}, @var{b}, @var{c}, @var{d}] =} besself (@dots{})
## @deftypefnx {Function File} {[@dots{}] =} besself (@dots{}, "z")
## Generate a Bessel filter.
## Default is a Laplace space (s) filter.
##
## [b,a] = besself(n, Wc)
## low pass filter with cutoff pi*Wc radians
##
## [b,a] = besself(n, Wc, 'high')
## high pass filter with cutoff pi*Wc radians
##
## [z,p,g] = besself(...)
## return filter as zero-pole-gain rather than coefficients of the
## numerator and denominator polynomials.
##
## [...] = besself(...,'z')
## return a discrete space (Z) filter, W must be less than 1.
##
## [a,b,c,d] = besself(...)
## return state-space matrices
##
## References:
##
## Proakis & Manolakis (1992). Digital Signal Processing. New York:
## Macmillan Publishing Company.
## @end deftypefn
function [a, b, c, d] = besself (n, w, varargin)
if (nargin > 4 || nargin < 2 || nargout > 4 || nargout < 2)
print_usage ();
endif
## interpret the input parameters
if (! (isscalar (n) && (n == fix (n)) && (n > 0)))
error ("besself: filter order N must be a positive integer");
endif
stop = false;
digital = false;
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 ("besself: expected [high|stop] or [s|z]");
endswitch
endfor
## FIXME: Band-pass and stop-band currently non-functional, remove
## this check once low-pass to band-pass transform is implemented.
if (! isscalar (w))
error ("besself: band-pass and stop-band filters not yet implemented");
endif
if (! ((numel (w) <= 2) && (rows (w) == 1 || columns (w) == 1)))
error ("besself: frequency must be given as WC or [WL, WH]");
elseif ((numel (w) == 2) && (w(2) <= w(1)))
error ("besself: W(1) must be less than W(2)");
endif
if (digital && ! all ((w >= 0) & (w <= 1)))
error ("besself: all elements of W must be in the range [0,1]");
elseif (! digital && ! all (w >= 0))
error ("besself: all elements of W must be in the range [0,inf]");
endif
## Prewarp to the band edges to s plane
if (digital)
T = 2; # sampling frequency of 2 Hz
w = 2 / T * tan (pi * w / T);
endif
## Generate splane poles for the prototype Bessel filter
[zero, pole, gain] = besselap (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
%% Test input validation
%!error [a, b] = besself ()
%!error [a, b] = besself (1)
%!error [a, b] = besself (1, 2, 3, 4, 5)
%!error [a, b] = besself (.5, .2)
%!error [a, b] = besself (3, .2, "invalid")
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