--- /dev/null
+## 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} {} ifft (@var{x})
+##
+## If @var{x} is a column vector, finds the IFFT 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
+## @seealso{ifft}
+
+function y = ifft(x)
+
+ if (nargin != 1)
+ error ("usage: y = ifft (x)");
+ endif
+
+ if (!isgalois(x))
+ error("ifft: argument must be a galois variable");
+ endif
+
+ n = 2^x.m - 1;
+ if (n > 255)
+ error ([ "ifft: argument must be in Galois Field GF(2^m), where", ...
+ " m is not greater than 8"]);
+ endif
+
+ alph = gf(2, x.m, x.prim_poly);
+ [nr,nc] = size(x);
+ if ((nc == 1) && (nr == n))
+ y = dftmtx(1/alph) * x;
+ elseif ((nc == n) && (nr == 1))
+ y = (dftmtx(1/alph) * x')';
+ else
+ error ("ifft: argument must be a vector in GF(2^m) of length 2^m-1");
+ endif
+
+endfunction