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1 ## Copyright (C) 1995, 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 3 of the License, or (at |
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8 ## your option) 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, see |
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17 ## <http://www.gnu.org/licenses/>. |
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18 |
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19 ## -*- texinfo -*- |
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20 ## @deftypefn {Function File} {} nbincdf (@var{x}, @var{n}, @var{p}) |
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21 ## For each element of @var{x}, compute the CDF at x of the Pascal |
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22 ## (negative binomial) distribution with parameters @var{n} and @var{p}. |
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23 ## |
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24 ## The number of failures in a Bernoulli experiment with success |
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25 ## probability @var{p} before the @var{n}-th success follows this |
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26 ## distribution. |
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27 ## @end deftypefn |
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28 |
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29 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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30 ## Description: CDF of the Pascal (negative binomial) distribution |
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31 |
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32 function cdf = nbincdf (x, n, p) |
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33 |
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34 if (nargin != 3) |
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35 print_usage (); |
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36 endif |
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37 |
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38 if (!isscalar(n) || !isscalar(p)) |
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39 [retval, x, n, p] = common_size (x, n, p); |
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40 if (retval > 0) |
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41 error ("nbincdf: x, n and p must be of common size or scalar"); |
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42 endif |
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43 endif |
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44 |
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45 cdf = zeros (size (x)); |
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46 |
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47 k = find (isnan (x) | (n < 1) | (n == Inf) | (n != round (n)) |
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48 | (p < 0) | (p > 1)); |
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49 if (any (k)) |
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50 cdf(k) = NaN; |
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51 endif |
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52 |
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53 k = find ((x == Inf) & (n > 0) & (n < Inf) & (n == round (n)) |
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54 & (p >= 0) & (p <= 1)); |
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55 if (any (k)) |
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56 cdf(k) = 1; |
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57 endif |
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58 |
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59 k = find ((x >= 0) & (x < Inf) & (x == round (x)) & (n > 0) |
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60 & (n < Inf) & (n == round (n)) & (p > 0) & (p <= 1)); |
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61 if (any (k)) |
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62 ## Does anyone know a better way to do the summation? |
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63 m = zeros (size (k)); |
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64 x = floor (x(k)); |
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65 y = cdf(k); |
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66 if (isscalar (n) && isscalar (p)) |
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67 while (1) |
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68 l = find (m <= x); |
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69 if (any (l)) |
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70 y(l) = y(l) + nbinpdf (m(l), n, p); |
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71 m(l) = m(l) + 1; |
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72 else |
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73 break; |
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74 endif |
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75 endwhile |
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76 else |
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77 n = n(k); |
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78 p = p(k); |
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79 while (1) |
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80 l = find (m <= x); |
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81 if (any (l)) |
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82 y(l) = y(l) + nbinpdf (m(l), n(l), p(l)); |
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83 m(l) = m(l) + 1; |
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84 else |
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85 break; |
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86 endif |
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87 endwhile |
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88 endif |
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89 cdf(k) = y; |
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90 endif |
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91 |
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92 endfunction |
