Kelvin functions

In applied mathematics, the Kelvin functions ber_ν(x) and bei_ν(x) are the real and imaginary parts, respectively, of

where x is real, and J_ν(z), is the ν order Bessel function of the first kind. Similarly, the functions Ker_ν(x) and Kei_ν(x) are the real and imaginary parts, respectively, of