1## Copyright (C) 2010  Soren Hauberg
2##
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)
6## any later version.
7##
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.
12##
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/>.
15
16## -*- texinfo -*-
17## @deftypefn {Function File} mpower (@var{KP}, @var{k})
18## Perform matrix power operation.
19## @end deftypefn
20
21function retval = mpower (KP, k)
22  ## Check input
23  if (nargin != 2)
24    print_usage ();
25  endif
26
27  if (! (ismatrix (KP) && isnumeric (KP)))
28    error ("mpower: first input argument must be a matrix");
29  endif
30
31  if (! isscalar (k))
32    error ("mpower: second input argument must be a scalar");
33  endif
34
35  ## Do the actual computation
36  if (issquare (KP.A) && issquare (KP.B) && k == round (k))
37    retval = kronprod (KP.A^k, KP.B^k);
38  elseif (issquare (KP))
39    ## XXX: Can we do something smarter here?
40    retval = full (KP)^k;
41  else
42    error ("for A^b, A must be square");
43  endif
44endfunction
45