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## Copyright (C) 1995, 1996 Kurt Hornik
##
## This program 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.
##
## This program 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 this file. If not, write to the Free Software Foundation,
## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
## usage: bincoeff (n, k)
##
## Returns the binomial coefficient of n and k.
## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
## Created: 8 October 1994
## Adapted-By: jwe
function b = bincoeff (n, k)
if (nargin != 2)
usage ("bincoeff (n, k)");
endif
[retval, n, k] = common_size (n, k);
if (retval > 0)
error ("bincoeff: n and k must be of common size or scalars");
endif
[r, c] = size (n);
s = r * c;
n = reshape (n, s, 1);
k = reshape (k, s, 1);
b = zeros (s, 1);
ind = find (! (k >= 0) | (k != real (round (k))) | isnan (n));
if (any (ind))
b(ind) = NaN * ones (length (ind), 1);
endif
ind = find (k == 0);
if (any (ind))
b(ind) = ones (length (ind), 1);
endif
ind = find ((k > 0) & ((n == real (round (n))) & (n < 0)));
if any (ind)
b(ind) = (-1) .^ k(ind) .* exp (lgamma (abs (n(ind)) + k(ind)) ...
- lgamma (k(ind) + 1) - lgamma (abs (n(ind))));
endif
ind = find ((k > 0) & ((n != real (round (n))) | (n >= k)));
if (length (ind) > 0)
b(ind) = exp (lgamma (n(ind) + 1) - lgamma (k(ind) + 1) ...
- lgamma (n(ind) - k(ind) + 1));
endif
## clean up rounding errors
ind = find (n == round (n));
if (any (ind))
b(ind) = round (b(ind));
endif
b = reshape (b, r, c);
endfunction
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