Computes the Airy function of the first kind.
- x (Double)
- The argument.
The value Ai(x).
Airy functions are solutions to the Airy differential equation:

The Airy functions appear in quantum mechanics in the semiclassical WKB solution to the wave functions in a potential.
For negative arguments, Ai(x) is oscilatory. For positive arguments, it decreases exponentially with increasing x.