std::expint, std::expintf, std::expintl
double expint( double arg );
double expint( float arg ); |
(1) | |
double expint( Integral arg );
|
(2) | |
As all special functions, expint
is only guaranteed to be available in <cmath>
if __STDCPP_MATH_SPEC_FUNCS__
is defined by the implementation to a value at least 201003L and if the user defines __STDCPP_WANT_MATH_SPEC_FUNCS__
before including any standard library headers.
Contents |
[edit] Parameters
arg | - | value of a floating-point or Integral type |
[edit] Return value
If no errors occur, value of the exponential integral ofarg
, that is -∫∞-arg
e-t |
t |
[edit] Error handling
Errors may be reported as specified in math_errhandling
- If the argument is NaN, NaN is returned and domain error is not reported
- If the argument is ±0, -∞ is returned
[edit] 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
[edit] Example
(works as shown with gcc 6.0)
Output:
Ei(0) = -inf Ei(1) = 1.89512 Gompetz constant = 0.596347
[edit] External links
Weisstein, Eric W. "Exponential Integral." From MathWorld--A Wolfram Web Resource.