binocdf.m

similer program for matlab

## Copyright (C) 1995, 1996, 1997, 2005, 2006, 2007 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.
##
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## 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} {} binocdf (@var{x}, @var{n}, @var{p})
## For each element of @var{x}, compute the CDF at @var{x} of the
## binomial distribution with parameters @var{n} and @var{p}.
## @end deftypefn

## Author: KH <[e-mail]>
## Description: CDF of the binomial distribution

function cdf = binocdf (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 ("binocdf: x, n and p must be of common size or scalar");
    endif
  endif

  sz = size (x);
  cdf = zeros (sz);

  k = find (isnan (x) | !(n >= 0) | (n != round (n))
	    | !(p >= 0) | !(p <= 1));
  if (any (k))
    cdf(k) = NaN;
  endif

  k = find ((x >= n) & (n >= 0) & (n == round (n))
	    & (p >= 0) & (p <= 1));
  if (any (k))
    cdf(k) = 1;
  endif

  k = find ((x >= 0) & (x < n) & (n == round (n))
	    & (p >= 0) & (p <= 1));
  if (any (k))
    tmp = floor (x(k));
    if (isscalar (n) && isscalar (p))
      cdf(k) = 1 - betainc (p, tmp + 1, n - tmp);
    else
      cdf(k) = 1 - betainc (p(k), tmp + 1, n(k) - tmp);
    endif
  endif

endfunction