--- /dev/null
+## Copyright (C) 2010 Soren Hauberg
+##
+## 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, 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 file. If not, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} uminus (@var{KP})
+## Returns the unary minus operator working on the Kronecker product @var{KP}.
+## This corresponds to @code{-@var{KP}} and simply returns the Kronecker
+## product with the sign of the smallest matrix in the product reversed.
+## @seealso{@@kronprod/uminus}
+## @end deftypefn
+
+function KP = uplus (KP)
+ if (nargin != 1)
+ print_usage ();
+ endif
+
+ if (!isa (KP, "kronprod"))
+ error ("uplus: input must be of class 'kronprod'");
+ endif
+
+ if (numel (KP.A) < numel (KP.B))
+ KP.A *= -1;
+ else
+ KP.B *= -1;
+ endif
+endfunction