## Copyright (C) 1996, 1997 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: hypergeometric_pdf (x, m, t, n) ## ## Compute the probability density function (PDF) at x of the ## hypergeometric distribution with parameters m, t, and n. This is the ## probability of obtaining x marked items when randomly drawing a ## sample of size n without replacement from a population of total size ## t containing m marked items. ## ## The arguments must be of common size or scalar. ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> ## Description: PDF of the hypergeometric distribution function pdf = hypergeometric_pdf (x, m, t, n) if (nargin != 4) usage ("hypergeometric_pdf (x, m, t, n)"); endif [retval, x, m, t, n] = common_size (x, m, t, n); if (retval > 0) error (["hypergeometric_pdf: ", ... "x, m, t, and n must be of common size or scalar"]); endif [r, c] = size (x); s = r * c; x = reshape (x, 1, s); m = reshape (m, 1, s); t = reshape (t, 1, s); n = reshape (n, 1, s); pdf = zeros * ones (1, s); ## everything in i1 gives NaN i1 = ((m < 0) | (t < 0) | (n <= 0) | (m != round (m)) | (t != round (t)) | (n != round (n)) | (m > t) | (n > t)); ## everything in i2 gives 0 unless in i1 i2 = ((x != round (x)) | (x < 0) | (x > m) | (n < x) | (n-x > t-m)); k = find (i1); if any (k) pdf (k) = NaN * ones (size (k)); endif k = find (!i1 & !i2); if any (k) pdf (k) = (bincoeff (m(k), x(k)) .* bincoeff (t(k)-m(k), n(k)-x(k)) ./ bincoeff (t(k), n(k))); endif endfunction

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