/usr/share/octave/packages/signal-1.3.0/impz.m is in octave-signal 1.3.0-1.
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 | ## Copyright (C) 1999 Paul Kienzle <pkienzle@users.sf.net>
##
## 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{x}, @var{t}] =} impz (@var{b})
## @deftypefnx {Function File} {[@var{x}, @var{t}] =} impz (@var{b}, @var{a})
## @deftypefnx {Function File} {[@var{x}, @var{t}] =} impz (@var{b}, @var{a}, @var{n})
## @deftypefnx {Function File} {[@var{x}, @var{t}] =} impz (@var{b}, @var{a}, @var{n}, @var{fs})
## @deftypefnx {Function File} {} impz (@dots{})
##
## Generate impulse-response characteristics of the filter. The filter
## coefficients correspond to the the z-plane rational function with
## numerator b and denominator a. If a is not specified, it defaults to
## 1. If n is not specified, or specified as [], it will be chosen such
## that the signal has a chance to die down to -120dB, or to not explode
## beyond 120dB, or to show five periods if there is no significant
## damping. If no return arguments are requested, plot the results.
##
## @seealso{freqz, zplane}
## @end deftypefn
## FIXME: Call equivalent function from control toolbox since it is
## probably more sophisticated than this one, and since it
## is silly to maintain two different versions of essentially
## the same thing.
function [x_r, t_r] = impz(b, a = [1], n = [], fs = 1)
if nargin == 0 || nargin > 4
print_usage;
endif
if isempty(n) && length(a) > 1
precision = 1e-6;
r = roots(a);
maxpole = max(abs(r));
if (maxpole > 1+precision) # unstable -- cutoff at 120 dB
n = floor(6/log10(maxpole));
elseif (maxpole < 1-precision) # stable -- cutoff at -120 dB
n = floor(-6/log10(maxpole));
else # periodic -- cutoff after 5 cycles
n = 30;
## find longest period less than infinity
## cutoff after 5 cycles (w=10*pi)
rperiodic = r(find(abs(r)>=1-precision & abs(arg(r))>0));
if !isempty(rperiodic)
n_periodic = ceil(10*pi./min(abs(arg(rperiodic))));
if (n_periodic > n)
n = n_periodic;
endif
endif
## find most damped pole
## cutoff at -60 dB
rdamped = r(find(abs(r)<1-precision));
if !isempty(rdamped)
n_damped = floor(-3/log10(max(abs(rdamped))));
if (n_damped > n)
n = n_damped;
endif
endif
endif
n = n + length(b);
elseif isempty(n)
n = length(b);
endif
if length(a) == 1
x = fftfilt(b/a, [1, zeros(1,n-1)]);
else
x = filter(b, a, [1, zeros(1,n-1)]);
endif
t = [0:n-1]/fs;
if nargout >= 1 x_r = x; endif
if nargout >= 2 t_r = t; endif
if nargout == 0
unwind_protect
title "Impulse Response";
if (fs > 1000)
t = t * 1000;
xlabel("Time (msec)");
else
xlabel("Time (sec)");
endif
plot(t, x, "^r;;");
unwind_protect_cleanup
title ("")
xlabel ("")
end_unwind_protect
endif
endfunction
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