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/*
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 * $Id: vbeta.cpp 1610 2014-02-05 06:00:52Z stevenmartell $
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 *
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 * Author: David Fournier
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 * Copyright (c) 2008-2012 Regents of the University of California
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 */
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/**
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 * \file
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 * Description not yet available.
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 */
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#include <fvar.hpp>
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/**
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 * Beta density function
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 * \param a shape parameter
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 * \param b shape parameter
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 * 
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 * Note that the mean of the distribution is given by 
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 * mu = a/(a+b), and the variance is ab/((a+b)^2 (a+b+1))
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 */
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dvariable beta(const prevariable& a,const prevariable& b )
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{
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  return exp(gammln(a)+gammln(b)-gammln(a+b));
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}