Phi.hpp

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#ifndef STAN_MATH_PRIM_FUN_PHI_HPP
#define STAN_MATH_PRIM_FUN_PHI_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/err.hpp>
#include <stan/math/prim/fun/constants.hpp>
#include <stan/math/prim/fun/erf.hpp>
#include <stan/math/prim/fun/erfc.hpp>
#include <stan/math/prim/fun/Phi.hpp>
#include <stan/math/prim/functor/apply_scalar_unary.hpp>
 
namespace stan {
namespace math {
 
inline double Phi(double x) {
  check_not_nan("Phi", "x", x);
  if (x < -37.5) {
    return 0;
  } else if (x < -5.0) {
    return 0.5 * erfc(-INV_SQRT_TWO * x);
  } else if (x > 8.25) {
    return 1;
  } else {
    return 0.5 * (1.0 + erf(INV_SQRT_TWO * x));
  }
}
 
struct Phi_fun {
  template <typename T>
  static inline auto fun(const T& x) {
    return Phi(x);
  }
};
 
template <
    typename T,
    require_all_not_nonscalar_prim_or_rev_kernel_expression_t<T>* = nullptr,
    require_not_var_matrix_t<T>* = nullptr>
inline auto Phi(const T& x) {
  return apply_scalar_unary<Phi_fun, T>::apply(x);
}
 
}  // namespace math
}  // namespace stan
 
#endif