std::expint, std::expintf, std::expintl

  1. Computes the exponential integral of arg.

# Declarations

double expint( double arg );
double expint( float arg );
double expint( long double arg );
float expintf( float arg );
long double expintl( long double arg );

double expint( IntegralType arg );

# Parameters

# Notes

Implementations that do not support TR 29124 but support TR 19768, provide this function in the header tr1/cmath and namespace std::tr1.

An implementation of this function is also available in boost.math.

# Example

#define __STDCPP_WANT_MATH_SPEC_FUNCS__ 1
#include <cmath>
#include <iostream>
 
int main()
{
    std::cout << "Ei(0) = " << std::expint(0) << '\n'
              << "Ei(1) = " << std::expint(1) << '\n'
              << "Gompetz constant = " << -std::exp(1) * std::expint(-1) << '\n';
}