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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} {} betapdf (@var{x}, @var{a}, @var{b}) |
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22 ## For each element of @var{x}, returns the PDF at @var{x} of the beta |
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23 ## distribution with parameters @var{a} and @var{b}. |
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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 Beta distribution |
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28 |
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29 function pdf = betapdf (x, a, b) |
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30 |
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31 if (nargin != 3) |
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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 (a) || !isscalar(b)) |
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36 [retval, x, a, b] = common_size (x, a, b); |
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37 if (retval > 0) |
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38 error ("betapdf: x, a and b 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 sz = size (x); |
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43 pdf = zeros (sz); |
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44 |
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45 k = find (!(a > 0) | !(b > 0) | isnan (x)); |
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46 if (any (k)) |
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47 pdf (k) = NaN; |
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48 endif |
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49 |
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50 k = find ((x > 0) & (x < 1) & (a > 0) & (b > 0)); |
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51 if (any (k)) |
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52 if (isscalar(a) && isscalar(b)) |
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53 pdf(k) = exp ((a - 1) .* log (x(k)) |
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54 + (b - 1) .* log (1 - x(k))) ./ beta (a, b); |
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55 else |
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56 pdf(k) = exp ((a(k) - 1) .* log (x(k)) |
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57 + (b(k) - 1) .* log (1 - x(k))) ./ beta (a(k), b(k)); |
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58 endif |
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59 endif |
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60 |
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61 endfunction |
