std:: comp_ellint_1, std:: comp_ellint_1f, std:: comp_ellint_1l

From cppreference.com
C++
Experimental
Mathematical special functions
double comp_ellint_1 ( double arg ) ;

double comp_ellint_1 ( float arg ) ;
double comp_ellint_1 ( long double arg ) ;
float comp_ellint_1f ( float arg ) ;

long double comp_ellint_1l ( long double arg ) ;
(1)
double comp_ellint_1 ( IntegralType arg ) ;
(2)
1) Computes the complete elliptic integral of the first kind of arg .
2) A set of overloads or a function template accepting an argument of any integral type . Equivalent to (1) after casting the argument to double .

As all special functions, comp_ellint_1 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.

Parameters

arg - value of a floating-point or integral type

Return value

If no errors occur, value of the complete elliptic integral of the first kind of arg , that is ellint_1(arg, π/2) , is returned.

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 |arg| > 1 , a domain error may occur.

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

(works as shown with gcc 6.0)

Run this code 
#define __STDCPP_WANT_MATH_SPEC_FUNCS__ 1
#include <cmath>
#include <iostream>
 
int main()
{
    double hpi = std::acos(-1) / 2;
    std::cout << "K(0) = " << std::comp_ellint_1(0) << '\n'
              << "π/2 = " << hpi << '\n'
              << "K(0.5) = " << std::comp_ellint_1(0.5) << '\n'
              << "F(0.5, π/2) = " << std::ellint_1(0.5, hpi) << '\n';
}

Output: 

K(0) = 1.5708
π/2 = 1.5708
K(0.5) = 1.68575
F(0.5, π/2) = 1.68575

External links

Weisstein, Eric W. "Complete Elliptic Integral of the First Kind." From MathWorld--A Wolfram Web Resource.

See also

(incomplete) elliptic integral of the first kind
(function)
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