Add a useful package (from Source forge) for octave

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

diff --git a/octave_packages/communications-1.1.1/@galois/convmtx.m b/octave_packages/communications-1.1.1/@galois/convmtx.m
new file mode 100644 (file)
index 0000000..2c423c1
--- /dev/null
+++ b/octave_packages/communications-1.1.1/@galois/convmtx.m
@@ -0,0 +1,47 @@
+## Copyright (C) 2003 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} {} convmtx (@var{a}, @var{n})
+##
+## Create matrix to perform repeated convolutions with the same vector
+## in a Galois Field. If @var{a} is a column vector and @var{x} is  a 
+## column vector of length @var{n}, in a Galois Field then 
+##
+## @code{convmtx(@var{a}, @var{n}) * @var{x}}
+##
+## gives the convolution of of @var{a} and @var{x} and is the
+## same as @code{conv(@var{a}, @var{x})}. The difference is if
+## many vectors are to be convolved with the same vector, then
+## this technique is possibly faster.
+##
+## Similarly, if @var{a} is a row vector and @var{x} is a row 
+## vector of length @var{n}, then
+##
+## @code{@var{x} * convmtx(@var{a}, @var{n})}
+##
+## is the same as @code{conv(@var{x}, @var{a})}.
+## @end deftypefn
+## @seealso{conv}
+
+function b = convmtx (a, n)
+
+  if (!isgalois (a))
+    error("convmtx: argument must be a galois variable");
+  endif
+
+  b = gf(convmtx(a.x,n), a.m, a.prim_poly);
+
+endfunction