X-Git-Url: https://git.creatis.insa-lyon.fr/pubgit/?p=CreaPhase.git;a=blobdiff_plain;f=octave_packages%2Fm%2Flinear-algebra%2Fvech.m;fp=octave_packages%2Fm%2Flinear-algebra%2Fvech.m;h=b1b278e7d327279164b747467f1366612d4d7d2b;hp=0000000000000000000000000000000000000000;hb=1c0469ada9531828709108a4882a751d2816994a;hpb=63de9f36673d49121015e3695f2c336ea92bc278
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+## Copyright (C) 1995-2012 Kurt Hornik
+## Copyright (C) 2009 VZLU Prague
+##
+## This file is part of Octave.
+##
+## Octave 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 of the License, or (at
+## your option) any later version.
+##
+## Octave 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 Octave; see the file COPYING. If not, see
+## .
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} vech (@var{x})
+## Return the vector obtained by eliminating all supradiagonal elements of
+## the square matrix @var{x} and stacking the result one column above the
+## other. This has uses in matrix calculus where the underlying matrix
+## is symmetric and it would be pointless to keep values above the main
+## diagonal.
+## @seealso{vec}
+## @end deftypefn
+
+## See Magnus and Neudecker (1988), Matrix differential calculus with
+## applications in statistics and econometrics.
+
+## Author KH
+## Created: 8 May 1995
+## Adapted-By: jwe
+
+function v = vech (x)
+
+ if (nargin != 1)
+ print_usage ();
+ endif
+
+ if (! issquare (x))
+ error ("vech: X must be square");
+ endif
+
+ n = rows (x);
+ slices = cellslices (x(:), (1:n) + n*(0:n-1), n*(1:n));
+ v = vertcat (slices{:});
+
+endfunction
+
+%!assert(all (vech ([1, 2, 3; 4, 5, 6; 7, 8, 9]) == [1; 4; 7; 5; 8; 9]));
+
+%!error vech ();
+
+%!error vech (1, 2);
+