/usr/share/octave/packages/signal-1.2.2/cheby1.m is in octave-signal 1.2.2-1build1.
This file is owned by root:root, with mode 0o644.
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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 | ## Copyright (C) 1999 Paul Kienzle <pkienzle@users.sf.net>
## 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/>.
## Generate an Chebyshev type I filter with Rp dB of pass band ripple.
##
## [b, a] = cheby1(n, Rp, Wc)
## low pass filter with cutoff pi*Wc radians
##
## [b, a] = cheby1(n, Rp, Wc, 'high')
## high pass filter with cutoff pi*Wc radians
##
## [b, a] = cheby1(n, Rp, [Wl, Wh])
## band pass filter with edges pi*Wl and pi*Wh radians
##
## [b, a] = cheby1(n, Rp, [Wl, Wh], 'stop')
## band reject filter with edges pi*Wl and pi*Wh radians
##
## [z, p, g] = cheby1(...)
## return filter as zero-pole-gain rather than coefficients of the
## numerator and denominator polynomials.
##
## [...] = cheby1(...,'s')
## return a Laplace space filter, W can be larger than 1.
##
## [a,b,c,d] = cheby1(...)
## return state-space matrices
##
## References:
##
## Parks & Burrus (1987). Digital Filter Design. New York:
## John Wiley & Sons, Inc.
function [a,b,c,d] = cheby1(n, Rp, W, varargin)
if (nargin>5 || nargin<3) || (nargout>4 || nargout<2)
print_usage;
endif
## interpret the input parameters
if (!(length(n)==1 && n == round(n) && n > 0))
error ("cheby1: filter order n must be a positive integer");
endif
stop = 0;
digital = 1;
for i=1:length(varargin)
switch varargin{i}
case 's', digital = 0;
case 'z', digital = 1;
case { 'high', 'stop' }, stop = 1;
case { 'low', 'pass' }, stop = 0;
otherwise, error ("cheby1: expected [high|stop] or [s|z]");
endswitch
endfor
[r, c]=size(W);
if (!(length(W)<=2 && (r==1 || c==1)))
error ("cheby1: frequency must be given as w0 or [w0, w1]");
elseif (!(length(W)==1 || length(W) == 2))
error ("cheby1: only one filter band allowed");
elseif (length(W)==2 && !(W(1) < W(2)))
error ("cheby1: first band edge must be smaller than second");
endif
if ( digital && !all(W >= 0 & W <= 1))
error ("cheby1: critical frequencies must be in (0 1)");
elseif ( !digital && !all(W >= 0 ))
error ("cheby1: critical frequencies must be in (0 inf)");
endif
if (Rp < 0)
error("cheby1: passband ripple must be positive decibels");
end
## 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 and zeros for the chebyshev type 1 filter
C = 1; # default cutoff frequency
epsilon = sqrt(10^(Rp/10) - 1);
v0 = asinh(1/epsilon)/n;
pole = exp(1i*pi*[-(n-1):2:(n-1)]/(2*n));
pole = -sinh(v0)*real(pole) + 1i*cosh(v0)*imag(pole);
zero = [];
## compensate for amplitude at s=0
gain = prod(-pole);
## if n is even, the ripple starts low, but if n is odd the ripple
## starts high. We must adjust the s=0 amplitude to compensate.
if (rem(n,2)==0)
gain = gain/10^(Rp/20);
endif
## 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
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