## Copyright (C) 1995, 1996, 1997  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 2, 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, write to the Free
## Software Foundation, 59 Temple Place - Suite 330, Boston, MA
## 02111-1307, USA.

## -*- texinfo -*-
## @deftypefn {Function File} {} binomial_rnd (@var{n}, @var{p}, @var{r}, @var{c})
## @deftypefnx {Function File} {} binomial_rnd (@var{n}, @var{p}, @var{sz})
## Return an @var{r} by @var{c}  or a @code{size (@var{sz})} matrix of 
## random samples from the binomial distribution with parameters @var{n}
## and @var{p}.  Both @var{n} and @var{p} must be scalar or of size
## @var{r} by @var{c}.
##
## If @var{r} and @var{c} are omitted, the size of the result matrix is
## the common size of @var{n} and @var{p}.
## @end deftypefn

## Author: KH <address@hidden>
## Description: Random deviates from the binomial distribution

function rnd = binomial_rnd (n, p, r, c)

  if (nargin > 1)
    if (!isscalar(n) || !isscalar(p)) 
      [retval, n, p] = common_size (n, p);
      if (retval > 0)
	error ("binomial_rnd: n and p must be of common size or scalar");
      endif
    endif
  endif

  if (nargin == 4)
    if (! (isscalar (r) && (r > 0) && (r == round (r))))
      error ("binomial_rnd: r must be a positive integer");
    endif
    if (! (isscalar (c) && (c > 0) && (c == round (c))))
      error ("binomial_rnd: c must be a positive integer");
    endif
    sz = [r, c];

    if (any (size (n) != 1) && ((length (size (n)) != length (sz)) ||
				any (size (n) != sz)))
      error ("binomial_rnd: n and must be scalar or of size [r, c]");
    endif
  elseif (nargin == 3)
    if (isscalar (r) && (r > 0))
      sz = [r, r];
    elseif (isvector(r) && all (r > 0))
      sz = r(:)';
    else
      error ("binomial_rnd: r must be a postive integer or vector");
    endif

    if (any (size (n) != 1) && ((length (size (n)) != length (sz)) ||
				any (size (n) != sz)))
      error ("binomial_rnd: n and must be scalar or of size sz");
    endif
  elseif (nargin == 2)
    sz = size(n);
  else
    usage ("binomial_rnd (n, p, r, c)");
  endif

  if (isscalar (n) && isscalar (p))
    if (find (!(n > 0) | !(n < Inf) | !(n == round (n)) |
              !(p >= 0) | !(p <= 1)))
      rnd = NaN * ones (sz);
    else
      nel = prod (sz);
      tmp = rand (n, nel);
      ind = (1 : n)' * ones (1, nel);
      rnd = (tmp < ones (n, nel) * p) & (ind <= ones (n, nel) * n);
      rnd = reshape(rnd, sz);
    endif
  else
    rnd = zeros (sz);

    k = find (!(n > 0) | !(n < Inf) | !(n == round (n)) |
              !(p >= 0) | !(p <= 1));
    if (any (k))
      rnd(k) = NaN;
    endif

    k = find ((n > 0) & (n < Inf) & (n == round (n)) & (p >= 0) & (p <= 1));
    if (any (k))
      N = max (n(k));
      L = length (k);
      tmp = rand (N, L);
      ind = (1 : N)' * ones (1, L);
      rnd(k) = sum ((tmp < ones (N, 1) * p(k)(:)') &
                    (ind <= ones (N, 1) * n(k)(:)'));
    endif
  endif

endfunction