sqrt.hpp

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#ifndef STAN_MATH_PRIM_FUN_SQRT_HPP
#define STAN_MATH_PRIM_FUN_SQRT_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>
 
namespace stan {
namespace math {
 
template <typename T, require_arithmetic_t<T>* = nullptr>
inline auto sqrt(T&& x) {
  return std::sqrt(x);
}
 
template <typename T, require_complex_bt<std::is_arithmetic, T>* = nullptr>
inline auto sqrt(T&& x) {
  return std::sqrt(x);
}
 
struct sqrt_fun {
  template <typename T>
  static inline auto fun(T&& x) {
    return sqrt(std::forward<T>(x));
  }
};
 
template <typename Container, require_ad_container_t<Container>* = nullptr>
inline auto sqrt(Container&& x) {
  return apply_scalar_unary<sqrt_fun, Container>::apply(
      std::forward<Container>(x));
}
 
template <typename Container,
          require_container_bt<std::is_arithmetic, Container>* = nullptr,
          require_not_var_matrix_t<Container>* = nullptr>
inline auto sqrt(Container&& x) {
  return apply_vector_unary<Container>::apply(
      std::forward<Container>(x), [](auto&& v) { return v.array().sqrt(); });
}
 
namespace internal {
template <typename V>
inline std::complex<V> complex_sqrt(const std::complex<V>& z) {
  auto m = sqrt(hypot(z.real(), z.imag()));
  auto at = 0.5 * atan2(z.imag(), z.real());
  return {m * cos(at), m * sin(at)};
}
}  // namespace internal
 
}  // namespace math
}  // namespace stan
 
#endif