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Return an exact answer on the home screen.
09-03-2015, 12:16 AM (This post was last modified: 09-03-2015 02:58 AM by pwarmuth.)
Post: #1
Return an exact answer on the home screen.
It would be nice if the Prime had the option to return either the decimal approximation of something like sqrt(2) + 1, or the exact answer while on the home screen. This is particularly the case when evaluating trig functions like sin(45). I'd like it to be able to display the answer as sqrt(2)/2 or it's numerical approximation, or even both simultaneously. If the answer contains an irrational constant, I'd like the option of having the answer contain that constant. Modern scientific calculators (no CAS) like the $40 Casio fx-991ex, $20 fx-113es, and even the venerable $20 TI 36x Pro do this, and I expect it from a scientific calculator that touts a textbook display.

I realize the CAS already does this, but you can't always use the CAS. Say for instance if a teacher locks it down for a test. Just because we don't have the capability to manipulate symbolic expressions doesn't mean that we should be limited to decimal approximations.
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09-03-2015, 12:54 PM
Post: #2
RE: Return an exact answer on the home screen.
You can force working with exact or approx expliciting exact( or approx(, from the help:

Code:
Syntax: exact(Expr)

Converts the expression to a rational or real expression. 

Example: exact(1.4141) returns 14141/10000

Code:
Syntax: approx(Expr,[Int])

Numerical evaluation of the first argument (we can give the number of digits as second argument).
approx(expression) works also and does the same thing.

Example: approx(2/3) returns 0.666666666667

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09-03-2015, 05:33 PM (This post was last modified: 09-03-2015 05:42 PM by Spybot.)
Post: #3
RE: Return an exact answer on the home screen.
Hello pwarmuth!

Maybe this help:
http://www.hpmuseum.org/forum/thread-18.html

Spybot.
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09-03-2015, 11:00 PM (This post was last modified: 09-03-2015 11:01 PM by pwarmuth.)
Post: #4
RE: Return an exact answer on the home screen.
These are both very interesting and useful suggestions, and I appreciate the help. The exact() command seems to do what I want for now, but I will keep that program in mind if I find a situation for which it does not. It seems to me that an option to default to exact() or approx() results in the home screen would be a useful addition.

Thank you guys for your time.
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09-03-2015, 11:49 PM (This post was last modified: 09-03-2015 11:49 PM by Tim Wessman.)
Post: #5
RE: Return an exact answer on the home screen.
What will most likely happen at some point is the a b/c key will ALSO cycle through as one of the options a QPI (that program) variant which will match values of sqrt, pi, etc. Right now it cycles decimal, fraction, mixed fraction, <insert qpi>, then back to decimal.

I also think it would be a good ideat extend that to let you toggle representations in other screens as well. Grapher, num table, etc.

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
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09-04-2015, 09:28 PM
Post: #6
RE: Return an exact answer on the home screen.
(09-03-2015 11:49 PM)Tim Wessman Wrote:  What will most likely happen at some point is the a b/c key will ALSO cycle through as one of the options a QPI (that program) variant which will match values of sqrt, pi, etc. Right now it cycles decimal, fraction, mixed fraction, <insert qpi>, then back to decimal.
I think, this would be a great enhancement.

Here's another (somewhat related) suggestion:

Playing with the emulator, I intuitively press the "a b/c" key trying to enter proper fractions or improper fractions (as this would be the key to enter fractions f.e. on Casio calculators). The Prime, however, cycles the stack X register contents through a number of display modes instead (which is definitely useful as well).
But wouldn't it be possible to combine both by preserving the Prime's behaviour for as long as the entry line is still empty, and switch the function of the "a b/c" key to an "enter fraction" mode as soon as someone starts entering a number? Not sure, if the stack X display toggle mode no longer being available in this specific situation would be great loss, but having some easy means to enter fractions would definitely be a plus.

Alternatively, couldn't the Prime be enhanced to support the "enter fraction" mode using the decimal dot "." as supported on some other calculators (like the HP-32SII or the WP 34S)?

1.2 -> 1.2 (normal real)
1.2.3 -> 1 2/3 (improper fraction)
.1.2. -> 1/2 (proper fraction)
1..2 -> 1/2 (proper fraction on the HP 32SII) or 1 0/2 (improper fraction on the WP 34S)
1.2. -> error (but perhaps could be made to be accepted as 1/2 as well)

I'm aware that I could use the "C" key on the Prime to enter fractions, but opening and reacting on a pop-up menu completely disturbs the input flow (old discussion "GUI vs. command line"), so I would rather like to "blindly" type in the number instead of navigating through menus.

Greetings,

Matthias


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