## 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})}.

## @seealso{conv}

## @end deftypefn

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