Mathematical constants

 

C++

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popcount (C++20)

endian (C++20)

 

Mathematical constants

 

Constants (since C++20)

Defined in header <numbers>
Defined in namespace std::numbers
e_v	the mathematical constant \(\small e\)e (variable template)
log2e_v	\(\log_{2}e\)log 2e (variable template)
log10e_v	\(\log_{10}e\)log 10e (variable template)
pi_v	the mathematical constant \(\pi\)π (variable template)
inv_pi_v	\(\frac1\pi\) 1 π (variable template)
inv_sqrtpi_v	\(\frac1{\sqrt\pi}\) 1 √π (variable template)
ln2_v	\(\ln{2}\)ln 2 (variable template)
ln10_v	\(\ln{10}\)ln 10 (variable template)
sqrt2_v	\(\sqrt2\)√2 (variable template)
sqrt3_v	\(\sqrt3\)√3 (variable template)
inv_sqrt3_v	\(\frac1{\sqrt3}\) 1 √3 (variable template)
egamma_v	the Euler–Mascheroni constant (variable template)
phi_v	the golden ratio Φ constant (\(\frac{1+\sqrt5}2\) 1 + √5 2 ) (variable template)
inline constexpr double e	e_v<double> (constant)
inline constexpr double log2e	log2e_v<double> (constant)
inline constexpr double log10e	log10e_v<double> (constant)
inline constexpr double pi	pi_v<double> (constant)
inline constexpr double inv_pi	inv_pi_v<double> (constant)
inline constexpr double inv_sqrtpi	inv_sqrtpi_v<double> (constant)
inline constexpr double ln2	ln2_v<double> (constant)
inline constexpr double ln10	ln10_v<double> (constant)
inline constexpr double sqrt2	sqrt2_v<double> (constant)
inline constexpr double sqrt3	sqrt3_v<double> (constant)
inline constexpr double inv_sqrt3	inv_sqrt3_v<double> (constant)
inline constexpr double egamma	egamma_v<double> (constant)
inline constexpr double phi	phi_v<double> (constant)

Notes

A program that instantiates a primary template of a mathematical constant variable template is ill-formed.

The standard library specializes mathematical constant variable templates for all floating-point types (i.e. float, double and long double).

A program may partially or explicitly specialize a mathematical constant variable template provided that the specialization depends on a program-defined type.

Feature-test macro:

__cpp_lib_math_constants

Example

Run this code

#include <cmath>
#include <iomanip>
#include <iostream>
#include <limits>
#include <numbers>
#include <string_view>
#include <functional>
 
using std::placeholders::_2;
template <class T>
constexpr auto operator^(T base, decltype(_2)) { return base * base; }
 
int main()
{
    using namespace std::numbers;
 
    std::cout << "The answer is " <<
        (((std::sin(e)^_2) + (std::cos(e)^_2)) + 
        std::pow(e, ln2) + std::sqrt(pi) * inv_sqrtpi +
        ((std::cosh(pi)^_2) - (std::sinh(pi)^_2)) +
        sqrt3 * inv_sqrt3 * log2e * ln2 * log10e * ln10 *
        pi * inv_pi + (phi * phi - phi)) *
        ((sqrt2 * sqrt3)^_2) << '\n';
 
    auto egamma_aprox = [] (unsigned const iterations) {
        long double s{}, m{2.0};
        for (unsigned c{2}; c != iterations; ++c, ++m) {
            const long double t{ std::riemann_zeta(m) / m };
            (c & 1) == 0 ? s += t : s -= t;
        }
        return s;
    };
 
    constexpr std::string_view γ {"0.577215664901532860606512090082402"};
 
    std::cout 
        << "γ as 10⁶ sums of ±ζ(m)/m   = "
        << egamma_aprox(1'000'000) << '\n'
        << "γ as egamma_v<float>       = "
        << std::setprecision(std::numeric_limits<float>::digits10 + 1)
        << egamma_v<float> << '\n'
        << "γ as egamma_v<double>      = "
        << std::setprecision(std::numeric_limits<double>::digits10 + 1)
        << egamma_v<double> << '\n'
        << "γ as egamma_v<long double> = "
        << std::setprecision(std::numeric_limits<long double>::digits10 + 1)
        << egamma_v<long double> << '\n'
        << "γ with " << γ.length() - 1 << " digits precision = " << γ << '\n';
}

Possible output:

The answer is 42
γ as 10⁶ sums of ±ζ(m)/m   = 0.577215
γ as egamma_v<float>       = 0.5772157
γ as egamma_v<double>      = 0.5772156649015329
γ as egamma_v<long double> = 0.5772156649015328606
γ with 34 digits precision = 0.577215664901532860606512090082402

See also

ratio (C++11)

represents exact rational fraction (class template)