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fft.m    54 lines (45 with data), 1.6 kB

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## Copyright (C) 2002 David Bateman
##
## 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} {} fft (@var{x})
##
## If @var{x} is a column vector, finds the FFT over the primitive element
## of the Galois Field of @var{x}. If @var{x} is in the Galois Field
## GF(2^@var{m}), then @var{x} must have @code{2^@var{m} - 1} elements.
## @end deftypefn
function y = fft (x)
if (nargin != 1)
print_usage ();
endif
if (!isgalois (x))
error ("fft: argument must be a galois variable");
endif
n = 2^x.m - 1;
if (n > 255)
error (["fft: argument must be in Galois Field GF(2^M)" ...
", where M is in the range [1,8]"]);
endif
alph = gf (2, x.m, x.prim_poly);
[nr, nc] = size (x);
if (nc == 1 && nr == n)
y = dftmtx (alph) * x;
elseif (nc == n && nr == 1)
y = (dftmtx (alph) * x')';
else
error ("fft: argument must be a vector in GF(2^M) of length 2^M-1");
endif
endfunction
%%Test input validation
%!error fft (gf (1, 12))