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annotate scripts/statistics/distributions/poisson_pdf.m @ 5307:4c8a2e4e0717

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[project @ 2005-04-26 19:24:27 by jwe]
author jwe
date Tue, 26 Apr 2005 19:24:47 +0000
parents 265d566cc770
children
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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, 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} {} poisson_pdf (@var{x}, @var{lambda})
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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 poisson distribution with parameter @var{lambda}.
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24 ## @end deftypefn
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25
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26 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
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27 ## Description: PDF of the Poisson distribution
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28
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29 function pdf = poisson_pdf (x, l)
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30
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31 if (nargin != 2)
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32 usage ("poisson_pdf (x, lambda)");
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33 endif
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34
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35 if (!isscalar (l))
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36 [retval, x, l] = common_size (x, l);
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37 if (retval > 0)
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38 error ("poisson_pdf: x and lambda must be of common size or scalar");
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39 endif
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40 endif
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41
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42 pdf = zeros (size (x));
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43
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44 k = find (!(l > 0) | isnan (x));
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45 if (any (k))
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46 pdf(k) = NaN;
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47 endif
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48
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49 k = find ((x >= 0) & (x < Inf) & (x == round (x)) & (l > 0));
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50 if (any (k))
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51 if (isscalar (l))
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52 pdf(k) = exp (x(k) .* log (l) - l - gammaln (x(k) + 1));
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53 else
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54 pdf(k) = exp (x(k) .* log (l(k)) - l(k) - gammaln (x(k) + 1));
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55 endif
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56 endif
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57
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58 endfunction