HP 80: What the heck is going on behind the curtain?
11-27-2019, 10:57 PM
Post: #3
 Dave Britten Senior Member Posts: 2,307 Joined: Dec 2013
RE: HP 80: What the heck is going on behind the curtain?
(11-27-2019 10:49 PM)Paul Dale Wrote:
(11-27-2019 10:35 PM)Dave Britten Wrote:  Press Shift-mean-x (the ->Sigma function) and now the sum of x is back in X, and n is back in Y. From here, you can continue using Sigma+/- to accumulate data. This reversal seems to happen instantly, unlike the forward calculation of mean and standard deviation, which makes it seem like it's pulling the numbers back out of temporary registers...

The reversal is multiplying the average by n and rearranging the stack. I doubt anything is stored in a temporary register.

Pauli

That does appear to be what's going on, based on a bit more playing. Shift-mean-x copies T to Y, then also multiplies X by T.

Sigma+ adds X to Y, X^2 to T, increments Z, and drops the stack, losing the last entered x value and copying sum of x^2 from T to Z. Sigma- presumably does the same, with subtraction and decrementing instead.
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 Messages In This Thread HP 80: What the heck is going on behind the curtain? - Dave Britten - 11-27-2019, 10:35 PM RE: HP 80: What the heck is going on behind the curtain? - Paul Dale - 11-27-2019, 10:49 PM RE: HP 80: What the heck is going on behind the curtain? - Dave Britten - 11-27-2019 10:57 PM RE: HP 80: What the heck is going on behind the curtain? - Dave Britten - 11-28-2019, 03:16 AM RE: HP 80: What the heck is going on behind the curtain? - teenix - 11-28-2019, 09:31 AM RE: HP 80: What the heck is going on behind the curtain? - Dave Britten - 11-28-2019, 12:59 PM RE: HP 80: What the heck is going on behind the curtain? - SlideRule - 11-28-2019, 07:30 PM

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