lmgamma.hpp

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#ifndef STAN__MATH__FUNCTIONS__LMGAMMA_HPP
#define STAN__MATH__FUNCTIONS__LMGAMMA_HPP

#include <boost/math/tools/promotion.hpp>
#include <stan/math/constants.hpp>
#include <boost/math/special_functions/gamma.hpp>

namespace stan {

  namespace math {

    template <typename T>
    inline typename boost::math::tools::promote_args<T>::type
    lmgamma(const int k, T x) {
      using boost::math::lgamma;
      typename boost::math::tools::promote_args<T>::type result 
        = k * (k - 1) * LOG_PI_OVER_FOUR;

      for (int j = 1; j <= k; ++j)
        result += lgamma(x + (1.0 - j) / 2.0);
      return result;
    }
      
  }
}
#endif