Here is a programming challenge for the RPN addicts.
Write a program that takes as input in the stack:
z: a
y: b
x: c
and outputs
y: (-b - sqrt(b^2 - 4ac))/(2a)
x: (-b + sqrt(b^2 - 4ac))/(2a)
(the solutions to the 2nd degree equation, assuming that they are real).
The program should use only the stack and the Last_x register, but no other registers.
The solution should be developed for the 11C or 15C or 32SII architecture (i.e., no HP48 extensions allowed, and in particular, no PICK instructions).
I have a 35-ish step solution that uses Last_x.
The solution is not particularily optimized, and I am not sure that Last_x is really needed.
The contest is open for the shortest solution,
and for a solution without Last_x!
Luca