1 ## Copyright (C) 2010 Soren Hauberg
3 ## This program is free software; you can redistribute it and/or modify
4 ## it under the terms of the GNU General Public License as published by
5 ## the Free Software Foundation; either version 3, or (at your option)
8 ## This program is distributed in the hope that it will be useful, but
9 ## WITHOUT ANY WARRANTY; without even the implied warranty of
10 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 ## General Public License for more details.
13 ## You should have received a copy of the GNU General Public License
14 ## along with this file. If not, see <http://www.gnu.org/licenses/>.
17 ## @deftypefn {Function File} trace (@var{KP})
18 ## Returns the trace of the Kronecker product @var{KP}.
20 ## If @var{KP} is a Kronecker product of two square matrices, the trace is
21 ## computed as the product of the trace of these two matrices. Otherwise the
22 ## trace is computed by forming the full matrix.
23 ## @seealso{@@kronprod/det, @@kronprod/rank, @@kronprod/full}
26 function retval = trace (KP)
31 if (!isa (KP, "kronprod"))
32 error ("trace: input must be of class 'kronprod'");
35 if (issquare (KP.A) && issquare (KP.B))
36 retval = trace (KP.A) * trace (KP.B);
38 ## XXX: Can we do something smarter here? Using 'eig' or 'svd'?
39 retval = trace (full (KP));