Whittaker equation

A linear homogeneous ordinary differential equation of the second order:

(*)

where the variables and the parameters may take arbitrary complex values. Equation (*) represents the reduced form of a degenerate hypergeometric equation and was first studied by E.T. Whittaker [1]. For the Whittaker equation is equivalent to the Bessel equation. If is not an integer, a fundamental system of solutions of the Whittaker equation consists of the functions and ; here is the Whittaker function (cf. Whittaker functions). For any value of the parameters the general solution of the Whittaker equation may be written in the form of a linear combination

where is the Whittaker function.

References

[1]	E.T. Whittaker, "An expression of certain known functions as generalized hypergeometric functions" Bull. Amer. Math. Soc. , 10 (1903) pp. 125–134
[2]	E.T. Whittaker, G.N. Watson, "A course of modern analysis" , Cambridge Univ. Press (1952)
[3]	H. Bateman (ed.) A. Erdélyi (ed.) , Higher transcendental functions , 1. The gamma function. The hypergeometric functions. Legendre functions , McGraw-Hill (1953)
[4]	A. Kratzer, W. Franz, "Transzendente Funktionen" , Akad. Verlagsgesell. Geest u. Portig K.-D. (1960)
[5]	E. Kamke, "Differentialgleichungen: Lösungen und Lösungsmethoden" , 1. Gewöhnliche Differentialgleichungen , Akad. Verlagsgesell. (1942)