update packages

[CreaPhase.git] / octave_packages / m / statistics / tests / chisquare_test_independence.m

diff --git a/octave_packages/m/statistics/tests/chisquare_test_independence.m b/octave_packages/m/statistics/tests/chisquare_test_independence.m
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+## Copyright (C) 1995-2012 Kurt Hornik
+##
+## 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
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{pval}, @var{chisq}, @var{df}] =} chisquare_test_independence (@var{x})
+## Perform a chi-square test for independence based on the contingency
+## table @var{x}.  Under the null hypothesis of independence,
+## @var{chisq} approximately has a chi-square distribution with
+## @var{df} degrees of freedom.
+##
+## The p-value (1 minus the CDF of this distribution at chisq) of the
+## test is returned in @var{pval}.
+##
+## If no output argument is given, the p-value is displayed.
+## @end deftypefn
+
+## Author: KH <Kurt.Hornik@wu-wien.ac.at>
+## Description: Chi-square test for independence
+
+function [pval, chisq, df] = chisquare_test_independence (x)
+
+  if (nargin != 1)
+    print_usage ();
+  endif
+
+  [r, s] = size (x);
+  df = (r - 1) * (s - 1);
+  n = sum (sum (x));
+  y = sum (x')' * sum (x) / n;
+  x = (x - y) .^2 ./ y;
+  chisq = sum (sum (x));
+  pval  = 1 - chi2cdf (chisq, df);
+
+  if (nargout == 0)
+    printf("  pval: %g\n", pval);
+  endif
+
+endfunction