I recently obtained a HP-80. While experimenting with various functions, I noticed that consecutive presses on (Yellow Shift)+(dot) changes the X value and the stack. Seems like doing some calculation, however couldn't find any information in the manual or elsewhere what type of function it is performing. Any idea? Thanks.
HP-80 Function Question
|
02-09-2012, 01:52 AM
02-10-2012, 03:00 PM
The result is the same as SIGMA+, and there are nothing in the user's manual, if I remember well. You can make some test to verify the results in the stack: Reg X SUM of data; Reg Y Num of data; Reg Z SUM of X^2; Reg T the same of Y reg. HTH
Ignazio Edited: 10 Feb 2012, 3:02 p.m.
02-10-2012, 04:27 PM
I was suspecting that however, after total clear:
Pressing sigma+ generates:
02-10-2012, 07:51 PM
That's what shift-dot does on the HP-80, whatever it is, starting from a clear stack:
T: 0 0 0 1 5 14 39 160 836 5192
Here is a BASIC program that produces the contents of stack registers X and Y: 5 CLS
02-11-2012, 02:27 PM
An interesting function. I wonder if HP was thinking about another financial or statistical function which later they decided not to include thus never made it to the keyboard. I am still trying to figure out what this calculation could be used for, expecially given the numbers displayed as an integer.
02-12-2012, 01:01 AM
Interestingly most of the first few terms are prime numbers: 1 2 3 5 11 26 66 227 1064 6257 62979 1251797 The next five terms are composites, however:
#include <iostream.h> RPL in exact mode on the HP 50g will handle those large numbers more easily than C++ though. ------------- Update: Yes, better on the HP 50g. No more primes, however. At least up to the 30th term:
\<< 0 1 0 { } 5 ROLL 1 SWAP
Edited: 12 Feb 2012, 4:43 p.m.
02-13-2012, 06:32 PM
Yet another implementation using Python:
def diff(xs):
I calculated the difference between sequent elements: [0, 1, 2, 3, 5, 11, 26, 66, 227, 1064] This shows that the 2nd difference is the same as the initial sequence squared and shifted.
Or as a recursive formula: This leads to the simple program:
x = [0, 1, 2] ... which produces the same result:
[0, 1, 2, 3, 5, 11, 26, 66, 227, 1064, 6257, 62979, 1251797]
I've tried in vain to use
Cheers Edited: 13 Feb 2012, 7:06 p.m.
02-13-2012, 06:57 PM
This is my understanding what both operations sigma+ and shift dot do:
T: T + X^2 However sigma+ seems to change its mind if you don't enter a number and starts to calculate the following instead:
T: T - X^2 I filled the stack with 1:
sigma+: T: 1 2 -2 -18 -43
shift dot: T: 1 2 6 22 71 I can't help but I think you just found a bug. Try the following:
shift CLEAR You'll get blinking 9.999999999 99 instead of 7. But you get the correct result when using shift dot instead.
Kind regards
02-13-2012, 08:50 PM
Very nice!
Quote: It's not in OEIS either. Regards, Gerson.
02-14-2012, 02:09 AM
Dear Thomas and Gerson,thank you very much for your responses and detailed analysis. I will use your directions and further experiment with this function. I have been away from my HP-80 last couple days. I also noticed that the sequence you enter the numbers (PV first vs n first) for PMT calculation gives different results. This may be due to limited number of registers HP-80 has and trying to utilize the stack as much as possible in order to solve the equation. I have feeling that shift dot is executing some sort of a subroutine which is being used as part of this solver, although it does seems like a bug since under the right conditions works better than the sigma+ function. Your responses have been very helpful, I have much more to think about now. Sincerely.
02-14-2012, 03:09 AM
Quote: You may ask them to add it. I wonder if they'll accept it.
Since after the first step of the recursion t' = z' we can just forget about t:
Just in case somebody might not believe that two sequences are equal when they agree on the first few elements.
Cheers
Edited: 14 Feb 2012, 3:13 a.m. |
« Next Oldest | Next Newest »
|