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## Diff of /inst/@gf/conv.m [000000] .. [05b386] Maximize Restore

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```--- a
+++ b/inst/@gf/conv.m
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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))
+
```