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## Copyright (C) 1995-2013 Kurt Hornik
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## This file is part of Octave.
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## Octave is free software; you can redistribute it and/or modify it
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## under the terms of the GNU General Public License as published by
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## the Free Software Foundation; either version 3 of the License, or (at
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## your option) any later version.
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## Octave is distributed in the hope that it will be useful, but
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## WITHOUT ANY WARRANTY; without even the implied warranty of
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## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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## General Public License for more details.
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## You should have received a copy of the GNU General Public License
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## along with Octave; see the file COPYING. If not, see
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## <http://www.gnu.org/licenses/>.
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## @deftypefn {Function File} {} autoreg_matrix (@var{y}, @var{k})
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## Given a time series (vector) @var{y}, return a matrix with ones in the
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## first column and the first @var{k} lagged values of @var{y} in the
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## other columns. I.e., for @var{t} > @var{k}, @code{[1,
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## @var{y}(@var{t}-1), @dots{}, @var{y}(@var{t}-@var{k})]} is the t-th row
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## of the result. The resulting matrix may be used as a regressor matrix
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## in autoregressions.
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## Author: KH <Kurt.Hornik@wu-wien.ac.at>
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## Description: Design matrix for autoregressions
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function X = autoreg_matrix (y, k)
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error ("autoreg_matrix: Y must be a vector");
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y = reshape (y, T, 1);
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X(:, j+1) = [(zeros (j, 1)); y(1:T-j)];
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%! assert (autoreg_matrix (A,K), B);
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%!error autoreg_matrix ()
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%!error autoreg_matrix (1)
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%!error autoreg_matrix (ones (4,1), 5)