/usr/include/ITK-4.9/vnl/vnl_beta.h is in libinsighttoolkit4-dev 4.9.0-4ubuntu1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | // This is core/vnl/vnl_beta.h
#ifndef vnl_beta_h_
#define vnl_beta_h_
//:
// \file
// \brief implementation of the beta function, also called the Euler integral of the first kind
// \author Gamze Tunali
#include "vnl_gamma.h"
#if 1 // implementation via vnl_log_gamma
//: Computation of beta function in terms of gamma function.
// Actually, this implementation refers to vnl_log_gamma,
// since this involves just a single call to std::exp instead of three.
template <class T>
inline double vnl_beta(T x, T y) {return vcl_exp(vnl_log_gamma(x)+vnl_log_gamma(y)-vnl_log_gamma(x+y)); }
#else // implementation via vnl_gamma; less efficient since it needs 3x vcl_exp
//: Computation of beta function in terms of gamma function.
template <class T>
inline double vnl_beta(T x, T y) {return (vnl_gamma(x)*vnl_gamma(y))/vnl_gamma(x+y); }
#endif
//: Computation of the log beta function in terms of the log gamma function.
// vnl_log_beta is just the std::log (natural logarithm) of the beta function.
template <class T>
inline double vnl_log_beta(T x, T y) {return vnl_log_gamma(x)+vnl_log_gamma(y)-vnl_log_gamma(x+y); }
#endif
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