A function used in the universal variables solution to the orbital equation. The Stumpff function is defined by
for k = 0, 1, 2, .... It satisfies the recurrence relation
The first two values are
References
Danby, J. M. Fundamentals of Celestial Mechanics, 2nd ed., rev. ed. Richmond, VA: Willmann-Bell, pp. 170-178, 1988.
