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conv.m    91 lines (78 with data), 2.6 kB

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## Copyright (C) 2011 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 2 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} {} conv (@var{a}, @var{b})
## Convolve two Galois vectors.
##
## @code{y = conv (a, b)} returns a vector of length equal to
## @code{length (a) + length (b) - 1}.
## If @var{a} and @var{b} are polynomial coefficient vectors, @code{conv}
## returns the coefficients of the product polynomial.
## @end deftypefn
## @seealso{deconv}
function y = conv (a, b)
if (nargin != 2)
usage ("conv(a, b)");
endif
if (!isgalois (a) && !isgalois (b))
error("conv: at least one argument must be a galois variable");
elseif (!isgalois (a))
a = gf(a, b._m, b._prim_poly);
elseif (!isgalois (b))
b = gf(b, a._m, a._prim_poly);
elseif (a._m != b._m && a._prim_poly != b._prim_poly)
error("conv: both vectors must be in the same galois field");
endif
if (min(size(a)) > 1 || min(size(b)) > 1)
error("conv: both arguments must be vectors");
endif
la = length (a);
lb = length (b);
ly = la + lb - 1;
## Ensure that both vectors are row vectors.
if (rows (a) > 1)
a = reshape (a, 1, la);
endif
if (rows (b) > 1)
b = reshape (b, 1, lb);
endif
## Use the shortest vector as the coefficent vector to filter.
if (la < lb)
if (ly > lb)
## Can't concatenate galois variables like this yet
## x = [b, (zeros (1, ly - lb))];
x = gf([b, (zeros (1, ly - lb))], b._m, b._prim_poly);
else
x = b;
endif
y = filter (a, 1, x);
else
if(ly > la)
## Can't concatenate galois variables like this yet
## x = [a, (zeros (1, ly - la))];
x = gf([a, (zeros (1, ly - la))], a._m, a._prim_poly);
else
x = a;
endif
y = filter (b, 1, x);
endif
endfunction
%!test
%! poly1 = gf([2,4,5,1],3);
%! poly2 = gf([1,2],3);
%! mulpoly = conv(poly1, poly2); ## multiplication
%! poly3 = [poly,remd] = deconv(mulpoly, poly2);
%! assert (isequal(poly1,poly3))
%! assert (!any (remd))