AIRY - Approximate the Airy functions  Ai(x), Bi(x) and their respective
       derivatives  Ai'(x), Bi'(x)

airya		return approximation of Ai(x)
airypa		return approximation of Ai'(x)
airyb		return approximation of Bi(x)
airybp		return approximation of Bi'(x)

Function Prototypes:
float airya (float x);
float airyap (float x);
float airyb (float x);
float airybp (float x);

Input:
x		value at which to evaluate Ai(x)

Returned:
airya		Ai(x)
airypa		Ai'(x)
airyb		Bi(x)
airybp		Bi'(x)

Reference:
The approximation is derived from tables and formulas in Abramowitz
and Stegun, p. 475-477.

Author:  Dave Hale, Colorado School of Mines, 06/06/89