Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / communications-1.1.1 / cosets.m

diff --git a/octave_packages/communications-1.1.1/cosets.m b/octave_packages/communications-1.1.1/cosets.m
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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} {} cosets (@var{m}, @var{prim})
+##
+## Finds the elements of GF(2^@var{m}) with primitive polynomial
+## @var{prim}, that share the same minimum polynomial. Returns a 
+## cell array of the paratitioning of GF(2^@var{m}).
+## @end deftypefn
+
+function c = cosets(m, prim)
+
+  if (nargin == 1)
+    prim = 0; ## This flags to use default primitive
+  elseif (nargin != 2)
+    error ("usage: c = cosets (m [, prim])");
+  endif
+
+  n = 2^m-1;
+  found = zeros(1,n);
+  c{1} = gf(1,m,prim);
+  found(1) = 1;
+  nc = 2;
+  f = log(gf(1:n,m,prim));
+
+  while ((!all(found)))
+    t = find(!found);
+    idx = f(t(find(f(t) == min(f(t).x)))).x;
+    set = idx;
+    r = rem(idx*2,n);
+    while (r > idx)
+      set =[set,r];
+      r = rem(r*2,n);
+    end
+    c{nc} = gf(sort(exp(gf(set,m,prim)).x),m,prim);
+    found(c{nc}.x) = ones(1,length(c{nc}));
+    nc = nc + 1;
+  end
+
+endfunction