cpp/numeric/special functions/cyl bessel k

@1-3@ Computes the (also known as modified Bessel function of the second kind) of  and. @A@ Additional overloads are provided for all other combinations of arithmetic types.

Return value
If no errors occur, value of the irregular modified cylindrical Bessel function (modified Bessel function of the second kind) of and, is returned, that is $K nu(x) =$ (where $I nu(x)$ is ) for $x≥0$ and non-integer ; for integer  a limit is used.

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 $nu≥128$, the behavior is implementation-defined.