Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/communications-1.1.1/@galois/roots.m b/octave_packages/communications-1.1.1/@galois/roots.m
new file mode 100644 (file)
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+++ b/octave_packages/communications-1.1.1/@galois/roots.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} {} roots (@var{v})
+##
+## For a vector @var{v} with @math{N} components, return
+## the roots of the polynomial over a Galois Field
+## @iftex
+## @tex
+## $$
+## v_1 z^{N-1} + \cdots + v_{N-1} z + v_N.
+## $$
+## @end tex
+## @end iftex
+## @ifinfo
+##
+## @example
+## v(1) * z^(N-1) + ... + v(N-1) * z + v(N).
+## @end example
+## @end ifinfo
+##
+## The number of roots returned and their value will be determined 
+## by the order and primitive polynomial of the Galios Field
+## @end deftypefn
+
+function r = roots (v)
+
+  if (nargin != 1)
+    error("usage: r = roots(v)");
+  endif
+
+  if (!isgalois(v))
+    error("roots: argument must be a galois variable");
+  endif
+
+  if (min (size (v)) > 1 || nargin != 1)
+    usage ("roots (v), where v is a galois vector");
+  endif
+
+  v = reshape (v, 1, length(v));
+  m = v.m;
+  prim_poly = v.prim_poly; 
+  n = 2^m - 1;
+  poly = v;
+  nr = 0;
+  t = 0;
+  r = [];        
+
+  while ((t <= n)  && (length(poly) > 1))
+    [npoly, nrem] = deconv(poly,gf([1,t],m,prim_poly));
+    if (any(nrem))
+      t = t + 1;
+    else
+      nr = nr + 1;
+      r(nr) = t;
+      poly = npoly;
+    endif
+  end
+
+  r = gf(r,m,prim_poly);        
+    
+endfunction