Hello all.

In light of a few things: the 34S development with its 8-register stack option, the long-standing established configuration of a 4-level RPN stack and the numerous ways which stack manipulations have been brainstormed and designed, I am wondering why four levels and not a five or even six register depth was implemented to begin with. This conundrum occurred to me after reading Palmer Hansen's 'HP Algebraic' article in the Jan 2011 edition of 'HP Solve' The reason I ask, in Example 2 on page 6, with the expression:

[ (3 + 1) (4 + 3) + (2 + 6) (4 + 6) ] / [ (2 + 3) (2 + 1) + (3 + 5)(4 + 2) ] = 108/63

is given an RPN algorithm which is quite elaborate and requires some twisting around because there are more intermediate results to work through (including handling the denominator initially):

2 ENTER 3 + 2 ENTER 1 + x 3 ENTER 5 + 4 ENTER 2 + x + 3 ENTER 1 + 4 ENTER 3 + x 2 ENTER 6 + RollDown x<>y / RollDown / x<>y RollDown 4 ENTER 6 + x +

I would've expected equation rearrangement from an Algebraic or AOS calculator and RPN is much more a natural problem solving approach. Two questions though: 1--are real-world formulas and mathematical expressions as complex as this one that require unintuitive rearrangement for RPN problem solving and 2--my original Q, would a stack size greater than four have been more efficient, versatile and sensible?

Thanks

*Edited: 25 June 2012, 8:01 p.m. *