RPN programming perplexity driving me nuts - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html) +--- Forum: General Forum (/forum-4.html) +--- Thread: RPN programming perplexity driving me nuts (/thread-9600.html) RPN programming perplexity driving me nuts - lemontea - 11-29-2017 08:53 PM Hi folks, Maybe it's my advancing years (lol) or something, but I just can't figure out what is going on. Wrote a very simply RPN routine on my 15C and the "bug" seems to replicate on 11C so must be a logic issue. I just want to calculate X - 1 ------ X^2 - 1 (x minus 1, divided by x-squared minus 1) So this is what I put in: LABEL A ENTER 1 - X <-> Y X^2 1 - / R/S The way I run it is just typing a number then issuing "f A" to run it. It seems not to work as intended if I do not press ENTER before issuing "f A" I thought the first ENTER (line 2) already puts the number I typed into both Y and X on the stack? And that I do not need to press ENTER before running the program, because whatever I typed (prior to issuing f-A) is already in the X register? ??? RE: RPN programming perplexity driving me nuts - Paul Dale - 11-29-2017 09:09 PM ENTER disables stack lift so the 1 on the next line overwrites X instead of raising it again. The solution is to ENTER ENTER or ENTER then a no-operation (x<>y e.g.) A quirk that survives. Pauli RE: RPN programming perplexity driving me nuts - hth - 11-29-2017 09:11 PM Try: X^2 LASTX 1 - X<>Y 1 - / The problem is that ENTER duplicates the number, but also disables stack lift. HÃ¥kan RE: RPN programming perplexity driving me nuts - Philippe - 11-29-2017 09:16 PM Hi, You can try here to see how the stack works : http://hp15c.com/web/hp15c.html Philippe RE: RPN programming perplexity driving me nuts - Dieter - 11-29-2017 10:13 PM (11-29-2017 08:53 PM)lemontea Wrote:  Maybe it's my advancing years (lol) or something, but I just can't figure out what is going on. This should have been resolved now: ENTER disables stack lift, so another ENTER is required. (11-29-2017 08:53 PM)lemontea Wrote:  I just want to calculate X - 1 ------ X^2 - 1 What about 1 + 1/x OK, except for x=1. ;-) Dieter RE: RPN programming perplexity driving me nuts - lemontea - 11-29-2017 11:13 PM Wow, thanks everyone. 3+ decades and somehow I got by without knowing that! Haha! RE: RPN programming perplexity driving me nuts - lemontea - 11-29-2017 11:15 PM (11-29-2017 09:16 PM)Philippe Wrote:  Hi, You can try here to see how the stack works : http://hp15c.com/web/hp15c.html Philippe Thanks, this is useful!