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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} {} poisspdf (@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@wu-wien.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 = poisspdf (x, l) |
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30 |
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31 if (nargin != 2) |
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32 print_usage (); |
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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 ("poisspdf: 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 |
