logit.hpp

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#ifndef STAN_MATH_PRIM_FUN_LOGIT_HPP
#define STAN_MATH_PRIM_FUN_LOGIT_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/fun/log.hpp>
#include <stan/math/prim/fun/to_ref.hpp>
#include <stan/math/prim/functor/apply_scalar_unary.hpp>
#include <stan/math/prim/functor/apply_vector_unary.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
template <typename T, require_floating_point_t<T>* = nullptr>
inline double logit(const T u) {
  return std::log(u / (1 - u));
}
 
template <typename T, require_integral_t<T>* = nullptr>
inline double logit(const T u) {
  return logit(static_cast<double>(u));
}
 
struct logit_fun {
  template <typename T>
  static inline auto fun(const T& x) {
    return logit(x);
  }
};
 
template <typename Container, require_ad_container_t<Container>* = nullptr>
inline auto logit(const Container& x) {
  return apply_scalar_unary<logit_fun, Container>::apply(x);
}
 
template <typename Container,
          require_container_bt<std::is_arithmetic, Container>* = nullptr>
inline auto logit(const Container& x) {
  return make_holder(
      [](const auto& v_ref) {
        return apply_vector_unary<ref_type_t<Container>>::apply(
            v_ref,
            [](const auto& v) { return (v.array() / (1 - v.array())).log(); });
      },
      to_ref(x));
}
 
}  // namespace math
}  // namespace stan
 
#endif