1 ## Copyright (C) 2003 David Bateman
3 ## This program is free software; you can redistribute it and/or modify it under
4 ## the terms of the GNU General Public License as published by the Free Software
5 ## Foundation; either version 3 of the License, or (at your option) any later
8 ## This program is distributed in the hope that it will be useful, but WITHOUT
9 ## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 ## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
13 ## You should have received a copy of the GNU General Public License along with
14 ## this program; if not, see <http://www.gnu.org/licenses/>.
17 ## @deftypefn {Function File} {} convmtx (@var{a}, @var{n})
19 ## Create matrix to perform repeated convolutions with the same vector
20 ## in a Galois Field. If @var{a} is a column vector and @var{x} is a
21 ## column vector of length @var{n}, in a Galois Field then
23 ## @code{convmtx(@var{a}, @var{n}) * @var{x}}
25 ## gives the convolution of of @var{a} and @var{x} and is the
26 ## same as @code{conv(@var{a}, @var{x})}. The difference is if
27 ## many vectors are to be convolved with the same vector, then
28 ## this technique is possibly faster.
30 ## Similarly, if @var{a} is a row vector and @var{x} is a row
31 ## vector of length @var{n}, then
33 ## @code{@var{x} * convmtx(@var{a}, @var{n})}
35 ## is the same as @code{conv(@var{x}, @var{a})}.
39 function b = convmtx (a, n)
42 error("convmtx: argument must be a galois variable");
45 b = gf(convmtx(a.x,n), a.m, a.prim_poly);