X-Git-Url: https://git.creatis.insa-lyon.fr/pubgit/?p=CreaPhase.git;a=blobdiff_plain;f=octave_packages%2Fm%2Fstatistics%2Fdistributions%2Fchi2pdf.m;fp=octave_packages%2Fm%2Fstatistics%2Fdistributions%2Fchi2pdf.m;h=18928de3fba9d7e308ff295ae58af13df856fc20;hp=0000000000000000000000000000000000000000;hb=1c0469ada9531828709108a4882a751d2816994a;hpb=63de9f36673d49121015e3695f2c336ea92bc278

diff --git a/octave_packages/m/statistics/distributions/chi2pdf.m b/octave_packages/m/statistics/distributions/chi2pdf.m
new file mode 100644
index 0000000..18928de
--- /dev/null
+++ b/octave_packages/m/statistics/distributions/chi2pdf.m
@@ -0,0 +1,72 @@
+## Copyright (C) 2012 Rik Wehbring
+## 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} {} chi2pdf (@var{x}, @var{n})
+## For each element of @var{x}, compute the probability density function
+## (PDF) at @var{x} of the chi-square distribution with @var{n} degrees
+## of freedom.
+## @end deftypefn
+
+## Author: TT <Teresa.Twaroch@ci.tuwien.ac.at>
+## Description: PDF of the chi-square distribution
+
+function pdf = chi2pdf (x, n)
+
+  if (nargin != 2)
+    print_usage ();
+  endif
+
+  if (!isscalar (n))
+    [retval, x, n] = common_size (x, n);
+    if (retval > 0)
+      error ("chi2pdf: X and N must be of common size or scalars");
+    endif
+  endif
+
+  if (iscomplex (x) || iscomplex (n))
+    error ("chi2pdf: X and N must not be complex");
+  endif
+
+  pdf = gampdf (x, n/2, 2);
+
+endfunction
+
+
+%!shared x,y
+%! x = [-1 0 0.5 1 Inf];
+%! y = [0, 1/2 * exp(-x(2:5)/2)];
+%!assert(chi2pdf (x, 2*ones(1,5)), y);
+%!assert(chi2pdf (x, 2), y);
+%!assert(chi2pdf (x, 2*[1 0 NaN 1 1]), [y(1) NaN NaN y(4:5)]);
+%!assert(chi2pdf ([x, NaN], 2), [y, NaN]);
+
+%% Test class of input preserved
+%!assert(chi2pdf (single([x, NaN]), 2), single([y, NaN]));
+%!assert(chi2pdf ([x, NaN], single(2)), single([y, NaN]));
+
+%% Test input validation
+%!error chi2pdf ()
+%!error chi2pdf (1)
+%!error chi2pdf (1,2,3)
+%!error chi2pdf (ones(3),ones(2))
+%!error chi2pdf (ones(2),ones(3))
+%!error chi2pdf (i, 2)
+%!error chi2pdf (2, i)
+