## [0404a4]: inst / @galois / ifft.m  Maximize  Restore  History

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 ``` 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``` ```## 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 . ## -*- 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. ## @seealso{ifft} ## @end deftypefn function y = ifft(x) if (nargin != 1) print_usage (); 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 ```