Lambert W function (for HP Prime)

[Albert Chan]

Does HP Prime have LambertW built-in ?

XCas> solve(x^2 = 2^x, x)

[-exp(-LambertW(ln(2)/2)), exp(-LambertW(-ln(2)/2)), exp(-LambertW(-ln(2)/2,-1))]

XCas> float(ans())

[-0.766664695962, 2.0, 4.0]

---

I think it is safe to use Halley's method for W.
Think of Halley's method as correction to Newton's method slope.
For W, slope correction is at most 50% (when x is *far* from -1/e)