# Standard library header <numbers> (C++20)

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This header is part of the numeric library.

### Mathematical constants (since C++20)

The header `<numbers>` provides several mathematical constants, such as std::numbers::pi or std::numbers::sqrt2

### Synopsis

    namespace std::numbers {
      template<class T> inline constexpr T e_v          = /* unspecified */;
      template<class T> inline constexpr T log2e_v      = /* unspecified */;
      template<class T> inline constexpr T log10e_v     = /* unspecified */;
      template<class T> inline constexpr T pi_v         = /* unspecified */;
      template<class T> inline constexpr T inv_pi_v     = /* unspecified */;
      template<class T> inline constexpr T inv_sqrtpi_v = /* unspecified */;
      template<class T> inline constexpr T ln2_v        = /* unspecified */;
      template<class T> inline constexpr T ln10_v       = /* unspecified */;
      template<class T> inline constexpr T sqrt2_v      = /* unspecified */;
      template<class T> inline constexpr T sqrt3_v      = /* unspecified */;
      template<class T> inline constexpr T inv_sqrt3_v  = /* unspecified */;
      template<class T> inline constexpr T egamma_v     = /* unspecified */;
      template<class T> inline constexpr T phi_v        = /* unspecified */;

      template<floating_point T> inline constexpr T e_v<T>          = /* see description */;
      template<floating_point T> inline constexpr T log2e_v<T>      = /* see description */;
      template<floating_point T> inline constexpr T log10e_v<T>     = /* see description */;
      template<floating_point T> inline constexpr T pi_v<T>         = /* see description */;
      template<floating_point T> inline constexpr T inv_pi_v<T>     = /* see description */;
      template<floating_point T> inline constexpr T inv_sqrtpi_v<T> = /* see description */;
      template<floating_point T> inline constexpr T ln2_v<T>        = /* see description */;
      template<floating_point T> inline constexpr T ln10_v<T>       = /* see description */;
      template<floating_point T> inline constexpr T sqrt2_v<T>      = /* see description */;
      template<floating_point T> inline constexpr T sqrt3_v<T>      = /* see description */;
      template<floating_point T> inline constexpr T inv_sqrt3_v<T>  = /* see description */;
      template<floating_point T> inline constexpr T egamma_v<T>     = /* see description */;
      template<floating_point T> inline constexpr T phi_v<T>        = /* see description */;

      inline constexpr double e          = e_v<double>;
      inline constexpr double log2e      = log2e_v<double>;
      inline constexpr double log10e     = log10e_v<double>;
      inline constexpr double pi         = pi_v<double>;
      inline constexpr double inv_pi     = inv_pi_v<double>;
      inline constexpr double inv_sqrtpi = inv_sqrtpi_v<double>;
      inline constexpr double ln2        = ln2_v<double>;
      inline constexpr double ln10       = ln10_v<double>;
      inline constexpr double sqrt2      = sqrt2_v<double>;
      inline constexpr double sqrt3      = sqrt3_v<double>;
      inline constexpr double inv_sqrt3  = inv_sqrt3_v<double>;
      inline constexpr double egamma     = egamma_v<double>;
      inline constexpr double phi        = phi_v<double>;
    }

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