The math library for the GNU basic calculator bc defines a few standard primitive functions:
s (x) The sine of x, x is in radians.
c (x) The cosine of x, x is in radians.
a (x) The arctangent of x, arctangent returns radians.
l (x) The natural logarithm of x.
e (x) The exponential function of raising e to the value x.
j (n,x) The bessel function of integer order n of x.
The primitive trigonometric functions make sense, because those are all you need to build all the other trigonometric functions, and natural log and exponential are all you need to do logarithmic/exponential calculations in other bases. But what's up with the Bessel function j? I'm posting this question here in hopes someone more familiar with Bessel functions than I understands what the motivation for including it in a basic calculator math library would be.
