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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
-
-