Four?! Why not more?

[Garth Wilson]

Is there really any need to name them?

[Bram]

(06-14-2021 12:08 PM)Steve Simpkin Wrote:  Of course if you want to have an RPN (not RPL) calculator with a stack limited only by memory,

you also could consider using the 'S3 RPN' calculator by Segitiga. (The one using the touch screen to get rid of the 2nd key.)

[Peet]

(06-14-2021 12:21 AM)Matt Agajanian Wrote:  ..., why not five or more registers?

As far as I know, every calculation with the 4 basic arithmetic operations and most algebraic functions can be solved with 3 stack levels. A fourth level may be necessary for functions with two operators such as y^x. I never heard about the need for a 5th level in any real-life arithmetic calculation (maybe somebody can construct one?).

RPL is a different concept, e.g. you can transfer the stack to arrays/matrix and back or store objects/programs/lists on the stack. For this you need an (so to say) unlimited stack.

(06-15-2021 06:32 PM)Bram Wrote:  you also could consider using the 'S3 RPN' calculator by Segitiga. (The one using the touch screen to get rid of the 2nd key.)

It seems to me that this calculator combines some disadvantages of RPL with RPN without having the advantages.

It has more than four stack levels, so no T register for recurring constants. It also has no Y, Z, T registers pre-filled with 0, so that pressing e.g. "+" gives an error message like RPL (just as annoying). Unlike RPL, however, it has a pre-filled X register so that "x^2" does not result in an empty stack error (a big improvement over the real RPL stack behavior). It has a LAST function, which does not work like LAST with RPL, but like LastX with RPN. It doesn't have a CLX like RPN but DROP like RPL. What I couldn't discover, however, was a practical use of the RPL stack.

(06-14-2021 02:55 AM)rprosperi Wrote:  Well, after X, Y, Z and T for TOP were used, there was no more room; you can't have a register past the top, there's just no room left.

Yes, that would be realy over the top.