update packages

[CreaPhase.git] / octave_packages / m / specfun / beta.m

diff --git a/octave_packages/m/specfun/beta.m b/octave_packages/m/specfun/beta.m
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+## Copyright (C) 1994-2012 John W. Eaton
+##
+## 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 {Mapping Function} {} beta (@var{a}, @var{b})
+## For real inputs, return the Beta function,
+## @tex
+## $$
+##  B (a, b) = {\Gamma (a) \Gamma (b) \over \Gamma (a + b)}.
+## $$
+## @end tex
+## @ifnottex
+##
+## @example
+## beta (a, b) = gamma (a) * gamma (b) / gamma (a + b).
+## @end example
+##
+## @end ifnottex
+## @end deftypefn
+
+## Author: KH <Kurt.Hornik@wu-wien.ac.at>
+## Created: 13 June 1993
+## Adapted-By: jwe
+
+function retval = beta (a, b)
+
+  if (nargin != 2)
+    print_usage ();
+  endif
+
+  if (any (size (a) != size (b)) && numel (a) != 1 && numel (b) != 1)
+    error ("beta: inputs A and B have inconsistent sizes");
+  endif
+
+  if (! isreal (a) || ! isreal (b))
+    error ("beta: inputs A and B must be real");
+  endif
+
+  retval = real (exp (gammaln (a) + gammaln (b) - gammaln (a+b)));
+
+endfunction
+
+%!test
+%! a=[1, 1.5, 2, 3];
+%! b=[4, 3, 2, 1];
+%! v1=beta(a,b);
+%! v2=beta(b,a);
+%! v3=gamma(a).*gamma(b)./gamma(a+b);
+%! assert(all(abs(v1-v2)<sqrt(eps)) && all(abs(v2-v3)<sqrt(eps)));
+
+%!error beta();
+
+%!error beta(1);
+
+%!assert (1, beta (1, 1))
+
+%!test
+%! a = 2:10;
+%! tol = 10 * max (a) * eps;
+%! assert (-a, beta (-1./a, 1), tol)
+%! assert (-a, beta (1, -1./a), tol)
+
+%!test
+%! a = 0.25 + (0:5) * 0.5;
+%! tol = 10 * max (a) * eps;
+%! assert (zeros (size (a)), beta (a, -a), tol)
+%! assert (zeros (size (a)), beta (-a, a), tol)