 Whittaker's equation is
It has a regular singular point at 0 and an irregular singular point at ∞.Two solutions are given by the Whittaker functions "M"κ,μ("z"), "W"κ,μ("z"), defined in terms of Kummer's confluent hypergeometric functions "M" and "U" by

The Whittaker functions formula_4 and formula_5 are the same as those with opposite values of , in other words considered as a function of at fixed and they are even functions.When and are real, the functions give real values for real and imaginary values of .