Besselk
Besselk (n, z)
The Besselk function returns the modified Bessel function of the second kind, Kn (z), of ordern and argument z. Supersedes the original bessK function, which is supported for backwards compatibility only.
If z is real, a real value is returned, which means that if z is also negative, Besselk returns NaN unless n is an integer.
For complex z a complex value is returned, and there are no restrictions on z except for possible overflow.
Details
The calculation is performed using the SLATEC library. The function supports fractional orders n, as well as real or complex arguments z.