update packages

[CreaPhase.git] / octave_packages / m / statistics / distributions / nbinpdf.m

diff --git a/octave_packages/m/statistics/distributions/nbinpdf.m b/octave_packages/m/statistics/distributions/nbinpdf.m
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+## 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} {} nbinpdf (@var{x}, @var{n}, @var{p})
+## For each element of @var{x}, compute the probability density function
+## (PDF) at @var{x} of the negative binomial distribution with
+## parameters @var{n} and @var{p}.
+##
+## When @var{n} is integer this is the Pascal distribution.  When
+## @var{n} is extended to real numbers this is the Polya distribution.
+## 
+## The number of failures in a Bernoulli experiment with success
+## probability @var{p} before the @var{n}-th success follows this
+## distribution.
+## @end deftypefn
+
+## Author: KH <Kurt.Hornik@wu-wien.ac.at>
+## Description: PDF of the Pascal (negative binomial) distribution
+
+function pdf = nbinpdf (x, n, p)
+
+  if (nargin != 3)
+    print_usage ();
+  endif
+
+  if (!isscalar (n) || !isscalar (p))
+    [retval, x, n, p] = common_size (x, n, p);
+    if (retval > 0)
+      error ("nbinpdf: X, N, and P must be of common size or scalars");
+    endif
+  endif
+
+  if (iscomplex (x) || iscomplex (n) || iscomplex (p))
+    error ("nbinpdf: X, N, and P must not be complex");
+  endif
+
+  if (isa (x, "single") || isa (n, "single") || isa (p, "single"))
+    pdf = NaN (size (x), "single");
+  else
+    pdf = NaN (size (x));
+  endif
+
+  ok = (x < Inf) & (x == fix (x)) & (n > 0) & (n < Inf) & (p >= 0) & (p <= 1);
+
+  k = (x < 0) & ok;
+  pdf(k) = 0;
+
+  k = (x >= 0) & ok;
+  if (isscalar (n) && isscalar (p))
+    pdf(k) = bincoeff (-n, x(k)) .* (p ^ n) .* ((p - 1) .^ x(k));
+  else
+    pdf(k) = bincoeff (-n(k), x(k)) .* (p(k) .^ n(k)) .* ((p(k) - 1) .^ x(k));
+  endif
+  
+
+endfunction
+
+
+%!shared x,y
+%! x = [-1 0 1 2 Inf];
+%! y = [0 1/2 1/4 1/8 NaN];
+%!assert(nbinpdf (x, ones(1,5), 0.5*ones(1,5)), y);
+%!assert(nbinpdf (x, 1, 0.5*ones(1,5)), y);
+%!assert(nbinpdf (x, ones(1,5), 0.5), y);
+%!assert(nbinpdf (x, [0 1 NaN 1.5 Inf], 0.5), [NaN 1/2 NaN 1.875*0.5^1.5/4 NaN], eps);
+%!assert(nbinpdf (x, 1, 0.5*[-1 NaN 4 1 1]), [NaN NaN NaN y(4:5)]);
+%!assert(nbinpdf ([x, NaN], 1, 0.5), [y, NaN]);
+
+%% Test class of input preserved
+%!assert(nbinpdf (single([x, NaN]), 1, 0.5), single([y, NaN]));
+%!assert(nbinpdf ([x, NaN], single(1), 0.5), single([y, NaN]));
+%!assert(nbinpdf ([x, NaN], 1, single(0.5)), single([y, NaN]));
+
+%% Test input validation
+%!error nbinpdf ()
+%!error nbinpdf (1)
+%!error nbinpdf (1,2)
+%!error nbinpdf (1,2,3,4)
+%!error nbinpdf (ones(3),ones(2),ones(2))
+%!error nbinpdf (ones(2),ones(3),ones(2))
+%!error nbinpdf (ones(2),ones(2),ones(3))
+%!error nbinpdf (i, 2, 2)
+%!error nbinpdf (2, i, 2)
+%!error nbinpdf (2, 2, i)
+