Strange behavior on G1 version 2.1.14588 (2021 05 05))
06-24-2021, 12:36 PM
Post: #1
 Over_score Junior Member Posts: 11 Joined: Jul 2018
Strange behavior on G1 version 2.1.14588 (2021 05 05))
Playing around with the sinc function (https://en.wikipedia.org/wiki/Sinc_function), I found a strange result:

In CAS mode, the result is correct.
How is that possible?
06-24-2021, 02:24 PM
Post: #2
 rprosperi Super Moderator Posts: 5,994 Joined: Dec 2013
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
Same result on a 48 and on a 50g (in approx mode, same as Prime Home).

It's an artifact of how these are calculated internally, probably using logs, though this latter part is just a wag.

In approx mode, SIN(Pi) is not 0.00, it's -2.06761537357E-13), so the math is correct.

--Bob Prosperi
06-24-2021, 02:41 PM
Post: #3
 Over_score Junior Member Posts: 11 Joined: Jul 2018
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
I understand that with a rounded value of pi (e.g. 3.14159265359), the result of sin(3.14159265359) is not 0 but -2.067…×10⁻¹³
But, sin(π) results in 0 in approx mode.
06-24-2021, 02:50 PM
Post: #4
 rprosperi Super Moderator Posts: 5,994 Joined: Dec 2013
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
Sorry, to be clear, my comment should have said "On the 48/50, In approx mode, SIN(Pi) is not 0.00, it's -2.06761537357E-13), so the math is correct."

If it's 0.00 on the Prime in Approx mode in Home, I'd guess that it's fudging the answer since the legacy 'pure' calculation shows the actual result, which is consistent with the value you reported.

Maybe Joe Horn can explain further...

--Bob Prosperi
06-24-2021, 04:23 PM
Post: #5
 ijabbott Senior Member Posts: 1,276 Joined: Jul 2015
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
HP Prime Lite 2.1.14591 on Android gives the correct approx result for SIN(π) → -2.06761537357E-13

— Ian Abbott
06-24-2021, 10:02 PM
Post: #6
 rprosperi Super Moderator Posts: 5,994 Joined: Dec 2013
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
The latest Android Prime Pro returns that same answer as well...

@Over_score - Where/how did you get 0 for SIN(Pi) in Approx mode (Home view)?

--Bob Prosperi
06-25-2021, 04:06 AM (This post was last modified: 06-25-2021 04:08 AM by Joe Horn.)
Post: #7
 Joe Horn Senior Member Posts: 1,985 Joined: Dec 2013
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
(06-24-2021 02:50 PM)rprosperi Wrote:  Maybe Joe Horn can explain further...

Yes, Home returns 0 for SIN(pi) only by explicitly looking for that expression and pretending to calculate the answer. It's sad and contrary to HP's previous philosophy, but more and more students are expecting to get results like this, so even HP is faking it now.

Also, note that SIN(pi)/pi also returns 0 in Home view if "Intelligent Math" mode is turned on (Home Settings, page 2, only in recent firmware versions). Although it's called "Intelligent Math" Mode, it should really be "Student Stupidity Compensator" Mode. It looks for certain patterns, and passes those through CAS for symbolic simplification. It sometimes returns what students expect, and sometimes doesn't, unpredictably. It will only be a reliable math tool when HP publishes a complete table of the lookup pattern inputs and outputs for "Intelligent Math" mode. And we all know when that will happen.

SIN(pi) and SIN(pi)/pi in CAS view do NOT return 0 when "Exact" mode (in CAS Settings) is turned off, since it uses the truncated 48-bit value of pi. When Exact mode is turned on, the symbol for pi is never evaluated; the expressions are simplified symbolically.

If any of the above is unclear, just holler.

<0|ɸ|0>
-Joe-
06-25-2021, 04:13 AM (This post was last modified: 06-25-2021 05:30 AM by dah145.)
Post: #8
 dah145 Junior Member Posts: 37 Joined: Aug 2020
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
Reproduced the result on the latest software, interestingly enough when Intelligent Math is checked the result is zero.

Edit: Already explained in the post above.

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06-25-2021, 07:25 AM
Post: #9
 Over_score Junior Member Posts: 11 Joined: Jul 2018
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
(06-24-2021 10:02 PM)rprosperi Wrote:  The latest Android Prime Pro returns that same answer as well...

@Over_score - Where/how did you get 0 for SIN(Pi) in Approx mode (Home view)?
I get this result in home view. By the way, in CAS view the result is correct.
06-25-2021, 03:30 PM (This post was last modified: 06-25-2021 03:43 PM by ijabbott.)
Post: #10
 ijabbott Senior Member Posts: 1,276 Joined: Jul 2015
RE: Strange behavior on G1 version 2.1.14588 (2021 05 05))
(06-25-2021 04:06 AM)Joe Horn Wrote:  Yes, Home returns 0 for SIN(pi) only by explicitly looking for that expression and pretending to calculate the answer. It's sad and contrary to HP's previous philosophy, but more and more students are expecting to get results like this, so even HP is faking it now.

Strangely (on the real calc, with "intelligent math" OFF), SIN(π*1) also returns 0, but SIN(π+0) doesn't!

EDIT: Maybe it should be considered a bug: "intelligent math" being used in some cases (and inconsistently so) even when the option is disabled.

— Ian Abbott
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