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[project @ 2005-03-03 05:25:23 by jwe]
author jwe
date Thu, 03 Mar 2005 05:26:57 +0000
parents 4b0f3b055331
children 4c8a2e4e0717
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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 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, 59 Temple Place - Suite 330, Boston, MA
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18 ## 02111-1307, USA.
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19
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20 ## -*- texinfo -*-
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21 ## @deftypefn {Function File} {} binomial_pdf (@var{x}, @var{n}, @var{p})
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22 ## For each element of @var{x}, compute the probability density function
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23 ## (PDF) at @var{x} of the binomial distribution with parameters @var{n}
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24 ## and @var{p}.
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25 ## @end deftypefn
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26
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27 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
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28 ## Description: PDF of the binomial distribution
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29
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30 function pdf = binomial_pdf (x, n, p)
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31
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32 if (nargin != 3)
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33 usage ("binomial_pdf (x, n, p)");
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34 endif
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35
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36 if (! isscalar (n) || ! isscalar (p))
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37 [retval, x, n, p] = common_size (x, n, p);
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38 if (retval > 0)
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39 error ("binomial_pdf: x, n and p must be of common size or scalar");
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40 endif
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41 endif
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42
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43 k = ((x >= 0) & (x <= n)
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44 & (x == round (x)) & (n == round (n))
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45 & (p >= 0) & (p <= 1));
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46
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47 pdf = zeros (size (x));
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48 pdf(! k) = NaN;
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49 if (any (k(:)))
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50 x = x(k);
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51 if (! isscalar (n))
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52 n = n(k);
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53 endif
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54 if (! isscalar (p))
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55 p = p(k);
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56 endif
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57 z = gammaln(n+1) - gammaln(x+1) - gammaln(n-x+1) + x.*log(p) + (n-x).*log(1-p);
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58 pdf(k) = exp (z);
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59 endif
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60
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61 endfunction