function vechA = vech(A)
% vech: Computes the column stacking operator which only stacks the elements on and below
%                the diagonal
%
% USAGE:
%
%       vechA = vech(A)
%
% REQUIRED INPUT:  A (nxn) matrix.
%
% REQUIRED OUTPUT: vechA (n(n+1)/2) vector which the elements on and below the diagonal of A.
%
%
%                       Written by: Anders Warne
%                                   New Area Wide Model Project
%                                   DG-R/EMO
%                                   European Central Bank (ECB)
%                                   Email: anders.warne@ecb.europa.eu
%                                   Copyright © 2006-2009 European Central Bank.
%
%                       First version: Januart 30, 2007.
%                        This version: May 23, 2008.
%
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%
% LICENSE INFORMATION:
%
%      YADA 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.
%
%      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 program.  If not, see <http://www.gnu.org/licenses/>.
%
%      YADA is released under the GNU General Public License, Version 3,
%      29 June 2007 <http://www.gnu.org/licenses/>. The current release of
%      the program was last modified by the ECB on the "This version" date
%      above.
%
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%
% CHANGELOG:
%
% * 13-11-2007: Updated the documentation.
%
% * 30-11-2007: Fixed a bug which prevented the function from being used with asymmetric matrices.
%
% * 23-5-2008:  Updated the documentation.
%
% * 21-01-2009: Updated the documentation.
%
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%

D = DuplicationMatrix(size(A,1));
vechA = D'*vec(tril(A));

%
% end of vech.m
%
