1 ## Copyright (C) 1996-2012 John W. Eaton
3 ## This file is part of Octave.
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13 ## General Public License for more details.
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20 ## @deftypefn {Function File} {[@var{beta}, @var{sigma}, @var{r}] =} ols (@var{y}, @var{x})
21 ## Ordinary least squares estimation for the multivariate model
25 ## $\bar{e} = 0$, and cov(vec($e$)) = kron ($s, I$)
28 ## @w{@math{y = x*b + e}} with
29 ## @math{mean (e) = 0} and @math{cov (vec (e)) = kron (s, I)}.
33 ## $y$ is a $t \times p$ matrix, $x$ is a $t \times k$ matrix,
34 ## $b$ is a $k \times p$ matrix, and $e$ is a $t \times p$ matrix.
37 ## @math{y} is a @math{t} by @math{p} matrix, @math{x} is a @math{t} by
38 ## @math{k} matrix, @math{b} is a @math{k} by @math{p} matrix, and
39 ## @math{e} is a @math{t} by @math{p} matrix.
42 ## Each row of @var{y} and @var{x} is an observation and each column a
45 ## The return values @var{beta}, @var{sigma}, and @var{r} are defined as
50 ## The OLS estimator for @math{b}.
52 ## $beta$ is calculated directly via $(x^Tx)^{-1} x^T y$ if the matrix $x^Tx$ is
56 ## @var{beta} is calculated directly via @code{inv (x'*x) * x' * y} if the
57 ## matrix @code{x'*x} is of full rank.
59 ## Otherwise, @code{@var{beta} = pinv (@var{x}) * @var{y}} where
60 ## @code{pinv (@var{x})} denotes the pseudoinverse of @var{x}.
63 ## The OLS estimator for the matrix @var{s},
67 ## @var{sigma} = (@var{y}-@var{x}*@var{beta})'
68 ## * (@var{y}-@var{x}*@var{beta})
69 ## / (@var{t}-rank(@var{x}))
74 ## The matrix of OLS residuals, @code{@var{r} = @var{y} - @var{x}*@var{beta}}.
76 ## @seealso{gls, pinv}
79 ## Author: Teresa Twaroch <twaroch@ci.tuwien.ac.at>
83 function [beta, sigma, r] = ols (y, x)
89 if (! (isnumeric (x) && isnumeric (y)))
90 error ("ols: X and Y must be numeric matrices or vectors");
93 if (ndims (x) != 2 || ndims (y) != 2)
94 error ("ols: X and Y must be 2-D matrices or vectors");
100 error ("ols: number of rows of X and Y must be equal");
110 ## Start of algorithm
117 beta = u \ (u' \ (x' * y));
120 if (isargout (2) || isargout (3))
125 ## z is of full rank, avoid the SVD in rnk
132 sigma = r' * r / (nr - rnk);
141 %! x = [x, ones(5,1)];
142 %! assert (ols(y,x), [3; 2], 50*eps)
147 %! [b, s, r] = ols (x, y);
148 %! assert (b, [1.4, 2], 2*eps);
149 %! assert (s, [0.2, 0; 0, 0], 2*eps);
150 %! assert (r, [-0.4, 0; 0.2, 0], 2*eps);
155 %! [b, s] = ols (x, y);
156 %! assert (b, [1.4, 2], 2*eps);
157 %! assert (s, [0.2, 0; 0, 0], 2*eps);
163 %! assert (b, [1.4, 2], 2*eps);
165 %% Test input validation
168 %!error ols (1, 2, 3);
169 %!error ols ([true, true], [1, 2]);
170 %!error ols ([1, 2], [true, true]);
171 %!error ols (ones (2,2,2), ones (2,2));
172 %!error ols (ones (2,2), ones (2,2,2));
173 %!error ols (ones(1,2), ones(2,2));