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1 ## Copyright (C) 1996, 1997 Kurt Hornik |
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2 ## |
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3 ## This file is part of Octave. |
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4 ## |
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5 ## Octave is free software; you can redistribute it and/or modify it |
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6 ## under the terms of the GNU General Public License as published by |
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7 ## the Free Software Foundation; either version 2, or (at your option) |
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8 ## any later version. |
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9 ## |
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10 ## Octave is distributed in the hope that it will be useful, but |
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 ## General Public License for more details. |
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14 ## |
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15 ## You should have received a copy of the GNU General Public License |
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16 ## along with Octave; see the file COPYING. If not, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} hygepdf (@var{x}, @var{m}, @var{t}, @var{n}) |
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22 ## Compute the probability density function (PDF) at @var{x} of the |
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23 ## hypergeometric distribution with parameters @var{m}, @var{t}, and |
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24 ## @var{n}. This is the probability of obtaining @var{x} marked items |
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25 ## when randomly drawing a sample of size @var{n} without replacement |
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26 ## from a population of total size @var{t} containing @var{m} marked items. |
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27 ## |
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28 ## The arguments must be of common size or scalar. |
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29 ## @end deftypefn |
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30 |
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31 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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32 ## Description: PDF of the hypergeometric distribution |
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33 |
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34 function pdf = hygepdf (x, m, t, n) |
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35 |
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36 if (nargin != 4) |
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37 print_usage (); |
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38 endif |
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39 |
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40 if (!isscalar (m) || !isscalar (t) || !isscalar (n)) |
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41 [retval, x, m, t, n] = common_size (x, m, t, n); |
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42 if (retval > 0) |
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43 error ("hygepdf: x, m, t, and n must be of common size or scalar"); |
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44 endif |
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45 endif |
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46 |
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47 pdf = zeros (size (x)); |
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48 |
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49 ## everything in i1 gives NaN |
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50 i1 = ((m < 0) | (t < 0) | (n <= 0) | (m != round (m)) | |
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51 (t != round (t)) | (n != round (n)) | (m > t) | (n > t)); |
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52 ## everything in i2 gives 0 unless in i1 |
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53 i2 = ((x != round (x)) | (x < 0) | (x > m) | (n < x) | (n-x > t-m)); |
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54 k = find (i1); |
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55 if (any (k)) |
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56 if (isscalar (m) && isscalar (t) && isscalar (n)) |
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57 pdf = NaN * ones ( size (x)); |
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58 else |
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59 pdf (k) = NaN; |
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60 endif |
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61 endif |
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62 k = find (!i1 & !i2); |
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63 if (any (k)) |
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64 if (isscalar (m) && isscalar (t) && isscalar (n)) |
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65 pdf (k) = (bincoeff (m, x(k)) .* bincoeff (t-m, n-x(k)) |
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66 / bincoeff (t, n)); |
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67 else |
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68 pdf (k) = (bincoeff (m(k), x(k)) .* bincoeff (t(k)-m(k), n(k)-x(k)) |
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69 ./ bincoeff (t(k), n(k))); |
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70 endif |
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71 endif |
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72 |
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73 endfunction |
