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annotate scripts/specfun/beta.m @ 8517:81d6ab3ac93c

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Allow documentation tobe built for other formats than tex and info
author sh@sh-laptop
date Wed, 14 Jan 2009 20:44:25 -0500
parents 8a939b217863
children e07e93c04080
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1 ## Copyright (C) 1994, 1995, 1996, 1997, 1999, 2000, 2002, 2005, 2006,
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2 ## 2007 John W. Eaton
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3 ##
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4 ## This file is part of Octave.
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5 ##
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6 ## Octave is free software; you can redistribute it and/or modify it
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7 ## under the terms of the GNU General Public License as published by
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8 ## the Free Software Foundation; either version 3 of the License, or (at
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9 ## your option) any later version.
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10 ##
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11 ## Octave is distributed in the hope that it will be useful, but
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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14 ## General Public License for more details.
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15 ##
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16 ## You should have received a copy of the GNU General Public License
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17 ## along with Octave; see the file COPYING. If not, see
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18 ## <http://www.gnu.org/licenses/>.
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19
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20 ## -*- texinfo -*-
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21 ## @deftypefn {Mapping Function} {} beta (@var{a}, @var{b})
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22 ## For real inputs, return the Beta function,
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23 ## @iftex
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24 ## @tex
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25 ## $$
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26 ## B (a, b) = {\Gamma (a) \Gamma (b) \over \Gamma (a + b)}.
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27 ## $$
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28 ## @end tex
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29 ## @end iftex
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30 ## @ifnottex
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31 ##
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32 ## @example
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33 ## beta (a, b) = gamma (a) * gamma (b) / gamma (a + b).
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34 ## @end example
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35 ## @end ifnottex
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36 ## @end deftypefn
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37
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38 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
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39 ## Created: 13 June 1993
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40 ## Adapted-By: jwe
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41
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42 function retval = beta (a, b)
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43
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44 if (nargin != 2)
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45 print_usage ();
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46 endif
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47
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48 if (any (size (a) != size (b)) && numel (a) != 1 && numel (b) != 1)
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49 error ("beta: inputs have inconsistent sizes.")
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50 endif
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51
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52 if (! isreal (a) || ! isreal (b))
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53 error ("beta: inputs must be real.")
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54 endif
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55
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56 retval = real (exp (gammaln (a) + gammaln (b) - gammaln (a+b)));
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57
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58 endfunction
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59
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60 %!test
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61 %! a=[1, 1.5, 2, 3];
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62 %! b=[4, 3, 2, 1];
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63 %! v1=beta(a,b);
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64 %! v2=beta(b,a);
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65 %! v3=gamma(a).*gamma(b)./gamma(a+b);
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66 %! assert(all(abs(v1-v2)<sqrt(eps)) && all(abs(v2-v3)<sqrt(eps)));
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67
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68 %!error beta();
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69
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70 %!error beta(1);
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71
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72 %!assert (1, beta (1, 1))
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73
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74 %!test
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75 %! a = 2:10;
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76 %! tol = 10 * max (a) * eps;
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77 %! assert (-a, beta (-1./a, 1), tol)
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78 %! assert (-a, beta (1, -1./a), tol)
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79
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80 %!test
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81 %! a = 0.25 + (0:5) * 0.5;
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82 %! tol = 10 * max (a) * eps;
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83 %! assert (zeros (size (a)), beta (a, -a), tol)
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84 %! assert (zeros (size (a)), beta (-a, a), tol)