Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / @galois / ifft.m

diff --git a/octave_packages/communications-1.1.1/@galois/ifft.m b/octave_packages/communications-1.1.1/@galois/ifft.m
new file mode 100644 (file)
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+++ b/octave_packages/communications-1.1.1/@galois/ifft.m
@@ -0,0 +1,51 @@
+## 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 <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