exp.hpp

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#ifndef STAN_MATH_PRIM_FUN_EXP_HPP
#define STAN_MATH_PRIM_FUN_EXP_HPP
 
#include <stan/math/prim/meta.hpp>
#include <stan/math/prim/fun/Eigen.hpp>
#include <stan/math/prim/functor/apply_scalar_unary.hpp>
#include <stan/math/prim/functor/apply_vector_unary.hpp>
#include <cmath>
#include <complex>
#include <limits>
 
namespace stan {
namespace math {
 
template <typename T, require_arithmetic_t<T>* = nullptr>
inline auto exp(T&& x) {
  return std::exp(x);
}
 
template <typename T, require_complex_bt<std::is_arithmetic, T>* = nullptr>
inline auto exp(T&& x) {
  return std::exp(x);
}
 
struct exp_fun {
  template <typename T>
  static inline auto fun(T&& x) {
    return exp(std::forward<T>(x));
  }
};
 
template <typename Container, require_ad_container_t<Container>* = nullptr>
inline auto exp(Container&& x) {
  return apply_scalar_unary<exp_fun, Container>::apply(
      std::forward<Container>(x));
}
 
template <typename Container,
          require_container_bt<std::is_arithmetic, Container>* = nullptr>
inline auto exp(Container&& x) {
  return apply_vector_unary<Container>::apply(
      std::forward<Container>(x), [](auto&& v) { return v.array().exp(); });
}
 
namespace internal {
template <typename V>
inline std::complex<V> complex_exp(const std::complex<V>& z) {
  if (is_inf(z.real()) && z.real() > 0) {
    if (is_nan(z.imag()) || z.imag() == 0) {
      // (+inf, nan), (+inf, 0)
      return z;
    } else if (is_inf(z.imag()) && z.imag() > 0) {
      // (+inf, +inf)
      return {z.real(), std::numeric_limits<double>::quiet_NaN()};
    } else if (is_inf(z.imag()) && z.imag() < 0) {
      // (+inf, -inf)
      return {std::numeric_limits<double>::quiet_NaN(),
              std::numeric_limits<double>::quiet_NaN()};
    }
  }
  if (is_inf(z.real()) && z.real() < 0
      && (is_nan(z.imag()) || is_inf(z.imag()))) {
    // (-inf, nan), (-inf, -inf), (-inf, inf)
    return {0, 0};
  }
  if (is_nan(z.real()) && z.imag() == -0.0) {
    // (nan, -0)
    return z;
  }
  V exp_re = exp(z.real());
  return {exp_re * cos(z.imag()), exp_re * sin(z.imag())};
}
}  // namespace internal
}  // namespace math
}  // namespace stan
 
#endif