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1 ## Copyright (C) 1998 by Nicol N. Schraudolph |
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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 {Mapping Function} {} betaln (@var{a}, @var{b}) |
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21 ## Return the log of the Beta function, |
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22 ## @iftex |
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23 ## @tex |
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24 ## $$ |
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25 ## B (a, b) = \log {\Gamma (a) \Gamma (b) \over \Gamma (a + b)}. |
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26 ## $$ |
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27 ## @end tex |
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28 ## @end iftex |
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29 ## @ifinfo |
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30 ## |
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31 ## @example |
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32 ## betaln (a, b) = gammaln (a) + gammaln (b) - gammaln (a + b) |
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33 ## @end example |
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34 ## @end ifinfo |
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35 ## @seealso{beta, betai, gammaln} |
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36 ## @end deftypefn |
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37 |
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38 ## Author: Nicol N. Schraudolph <nic@idsia.ch> |
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39 ## Created: 06 Aug 1998 |
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40 ## Keywords: log beta special function |
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41 |
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42 function retval = betaln (a, b) |
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43 if (nargin != 2) |
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44 print_usage (); |
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45 endif |
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46 |
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47 retval = gammaln (a) + gammaln (b) - gammaln (a + b); |
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48 endfunction |
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49 |
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50 %!assert (betaln(3,4),log(beta(3,4)),eps) |
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51 |
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52 %!error (betaln(1.)) |
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53 %!error (betaln(1.,1.,1.)) |
