lambert_w.hpp

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#ifndef STAN_MATH_PRIM_FUN_LAMBERT_W_HPP
#define STAN_MATH_PRIM_FUN_LAMBERT_W_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/functor/apply_scalar_unary.hpp>
#include <stan/math/prim/fun/boost_policy.hpp>
#include <boost/math/special_functions/lambert_w.hpp>
 
namespace stan {
namespace math {
 
template <typename T, require_arithmetic_t<T>* = nullptr>
inline double lambert_w0(const T& x) {
  return boost::math::lambert_w0(x, boost_policy_t<>());
}
 
template <typename T, require_arithmetic_t<T>* = nullptr>
inline double lambert_wm1(const T& x) {
  return boost::math::lambert_wm1(x, boost_policy_t<>());
}
 
namespace internal {
 
struct lambert_w0_fun {
  template <typename T>
  static inline auto fun(const T& x) {
    return lambert_w0(x);
  }
};
 
struct lambert_wm1_fun {
  template <typename T>
  static inline auto fun(const T& x) {
    return lambert_wm1(x);
  }
};
}  // namespace internal
 
template <typename T, require_not_stan_scalar_t<T>* = nullptr,
          require_not_var_matrix_t<T>* = nullptr>
inline auto lambert_w0(const T& x) {
  return apply_scalar_unary<internal::lambert_w0_fun, T>::apply(x);
}
 
template <typename T, require_not_stan_scalar_t<T>* = nullptr,
          require_not_var_matrix_t<T>* = nullptr>
inline auto lambert_wm1(const T& x) {
  return apply_scalar_unary<internal::lambert_wm1_fun, T>::apply(x);
}
 
}  // namespace math
}  // namespace stan
 
#endif