Add a useful package (from Source forge) for octave

[CreaPhase.git] / octave_packages / linear-algebra-2.2.0 / @kronprod / trace.m

diff --git a/octave_packages/linear-algebra-2.2.0/@kronprod/trace.m b/octave_packages/linear-algebra-2.2.0/@kronprod/trace.m
new file mode 100644 (file)
index 0000000..75be2a5
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+++ b/octave_packages/linear-algebra-2.2.0/@kronprod/trace.m
@@ -0,0 +1,41 @@
+## 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