lmgamma.hpp

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#ifndef STAN_MATH_PRIM_FUN_LMGAMMA_HPP
#define STAN_MATH_PRIM_FUN_LMGAMMA_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/fun/constants.hpp>
#include <stan/math/prim/fun/lgamma.hpp>
#include <stan/math/prim/fun/sum.hpp>
#include <stan/math/prim/functor/apply_scalar_binary.hpp>
 
namespace stan {
namespace math {
 
template <typename T, require_arithmetic_t<T>* = nullptr>
inline return_type_t<T> lmgamma(int k, T x) {
  return_type_t<T> result = k * (k - 1) * LOG_PI_OVER_FOUR;
 
  return result + sum(lgamma(x + (1 - Eigen::ArrayXd::LinSpaced(k, 1, k)) / 2));
}
 
template <typename T1, typename T2, require_any_container_t<T1, T2>* = nullptr>
inline auto lmgamma(T1&& a, T2&& b) {
  return apply_scalar_binary(
      [](auto&& c, auto&& d) {
        return lmgamma(std::forward<decltype(c)>(c),
                       std::forward<decltype(d)>(d));
      },
      std::forward<T1>(a), std::forward<T2>(b));
}
 
}  // namespace math
}  // namespace stan
#endif