/usr/share/octave/packages/signal-1.3.2/tf2sos.m is in octave-signal 1.3.2-5.
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 | ## Copyright (C) 2005 Julius O. Smith III <jos@ccrma.stanford.edu>
##
## 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{sos}, @var{g}] =} tf2sos (@var{b}, @var{a})
## @deftypefnx {Function File} {@var{sos} =} tf2sos (@var{b}, @var{a})
## Convert direct-form filter coefficients to series second-order sections.
##
## INPUTS:
##
## @var{b} and @var{a} are vectors specifying the digital filter
## @math{H(z) = B(z)/A(z)}. See @code{filter} for documentation of the @var{b}
## and @var{a} filter coefficients.
##
## RETURNED:
## @itemize
## @item
## @var{sos} = matrix of series second-order sections, one per row:
## @example
## @var{sos} = [@var{b1}.' @var{a1}.'; ...; @var{bn}.' @var{an}.']
## @end example
## where
## @code{@var{B1}.' = [b0 b1 b2] and @var{A1}.' = [1 a1 a2]} for
## section 1, etc. The b0 entry must be nonzero for each section (zeros at
## infinity not supported).
## @item
## @var{g} is an overall gain factor that effectively scales
## any one of the @var{B}i vectors.
## @end itemize
##
## If called with only one output argument, the overall filter gain is
## applied to the first second-order section in the matrix @var{sos}.
##
## EXAMPLE:
## @example
## B = [1 0 0 0 0 1];
## A = [1 0 0 0 0 .9];
## [sos, g] = tf2sos (B, A)
##
## sos =
##
## 1.00000 0.61803 1.00000 1.00000 0.60515 0.95873
## 1.00000 -1.61803 1.00000 1.00000 -1.58430 0.95873
## 1.00000 1.00000 -0.00000 1.00000 0.97915 -0.00000
##
## g = 1
## @end example
##
## @seealso{sos2tf, zp2sos, sos2pz, zp2tf, tf2zp}
## @end deftypefn
function [sos,g] = tf2sos (B, A)
[z,p,k] = tf2zp(B(:)',A(:)');
if (nargout < 2)
sos = zp2sos(z,p,k);
else
[sos,g] = zp2sos(z,p,k);
endif
endfunction
%!test
%! B=[1 0 0 0 0 1]; A=[1 0 0 0 0 .9];
%! [sos,g] = tf2sos(B,A);
%! [Bh,Ah] = sos2tf(sos,g);
%! assert({Bh,Ah},{B,A},100*eps);
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