/usr/share/octave/packages/3.2/linear-algebra-2.1.0/@kronprod/trace.m is in octave-linear-algebra 2.1.0-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | ## 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} trace (@var{KP})
## Returns the trace of the Kronecker product @var{KP}.
##
## If @var{KP} is a Kronecker product of two square matrices, the trace is
## computed as the product of the trace of these two matrices. Otherwise the
## trace is computed by forming the full matrix.
## @seealso{@@kronprod/det, @@kronprod/rank, @@kronprod/full}
## @end deftypefn
function retval = trace (KP)
if (nargin != 1)
print_usage ();
endif
if (!isa (KP, "kronprod"))
error ("trace: input must be of class 'kronprod'");
endif
if (issquare (KP.A) && issquare (KP.B))
retval = trace (KP.A) * trace (KP.B);
else
## XXX: Can we do something smarter here? Using 'eig' or 'svd'?
retval = trace (full (KP));
endif
endfunction
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