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+--- 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.
Håkan
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!