beta.hpp

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#ifndef STAN_MATH_PRIM_FUN_BETA_HPP
#define STAN_MATH_PRIM_FUN_BETA_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/fun/exp.hpp>
#include <stan/math/prim/fun/lgamma.hpp>
#include <stan/math/prim/functor/apply_scalar_binary.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
template <typename T1, typename T2, require_all_arithmetic_t<T1, T2>* = nullptr>
inline return_type_t<T1, T2> beta(const T1 a, const T2 b) {
  using std::exp;
  return exp(lgamma(a) + lgamma(b) - lgamma(a + b));
}
 
template <typename T1, typename T2, require_any_container_t<T1, T2>* = nullptr,
          require_all_not_var_matrix_t<T1, T2>* = nullptr>
inline auto beta(const T1& a, const T2& b) {
  return apply_scalar_binary(
      a, b, [](const auto& c, const auto& d) { return beta(c, d); });
}
 
}  // namespace math
}  // namespace stan
 
#endif