std::sph_bessel, std::sph_besself, std::sph_bessell

float       sph_bessel ( unsigned int n, float x );
double      sph_bessel ( unsigned int n, double x );
long double sph_bessel ( unsigned int n, long double x );

/* floating-point-type */ sph_bessel( unsigned int n,
                                      /* floating-point-type */ x );

float       sph_besself( unsigned int n, float x );

long double sph_bessell( unsigned int n, long double x );

template< class Integer >
double      sph_bessel ( unsigned int n, Integer x );

double

Parameters

Return value

If no errors occur, returns the value of the spherical Bessel function of the first kind of n and x, that is j
n(x) = (π/2x)1/2
J
n+1/2(x) where J
n(x) is std::cyl_bessel_j(n, x) and x≥0.

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 n≥128, the behavior is implementation-defined.

Notes

Implementations that do not support C++17, but support ISO 29124:2010, provide this function 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.

Implementations that do not support ISO 29124:2010 but support TR 19768:2007 (TR1), provide this function in the header tr1/cmath and namespace std::tr1.

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

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::sph_bessel(int_num, num) has the same effect as std::sph_bessel(int_num, static_cast<double>(num)).

Example

#include <cmath>
#include <iostream>
 
int main()
{
    // spot check for n == 1
    double x = 1.2345;
    std::cout << "j_1(" << x << ") = " << std::sph_bessel(1, x) << '\n';
 
    // exact solution for j_1
    std::cout << "sin(x)/x² - cos(x)/x = "
              << std::sin(x) / (x * x) - std::cos(x) / x << '\n';
}

j_1(1.2345) = 0.352106
sin(x)/x² - cos(x)/x = 0.352106

See also

External links