/usr/share/octave/packages/signal-1.3.0/dftmtx.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 | ## Copyright (C) 2003 David Bateman <adb014@gmail.com>
##
## 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{d} =} dftmtx (@var{n})
## Compute the @var{n}-by-@var{n} Fourier transformation matrix. This is
## the matrix @var{d} such that the Fourier transform of a column vector of
## length @var{n} is given by @code{dftmtx(@var{n}) * @var{x}} and the
## inverse Fourier transform is given by @code{inv(dftmtx(@var{n})) * @var{x}}.
##
## In general this is less efficient than calling the @code{fft} and
## @code{ifft} functions directly.
## @seealso{fft, ifft}
## @end deftypefn
function d = dftmtx(n)
if (nargin != 1)
print_usage;
elseif (!isscalar(n))
error ("dftmtx: argument must be scalar");
endif
d = fft(eye(n));
endfunction
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