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Error with exponential fractions
11-11-2014, 08:46 PM
Post: #1
Error with exponential fractions
When I tried to do e^(-t)/e^(t) with t being a variable the answer should be 1/e^(2*t) but in the hp prime the answer is 1/e^(t^(2)). But I think it's a visual problem because when I integrate the expression it gives the correct answer.

I have attached an image showing it.

   
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11-11-2014, 08:57 PM (This post was last modified: 11-11-2014 09:25 PM by Gilles.)
Post: #2
RE: Error with exponential fractions
(11-11-2014 08:46 PM)Juan.C Wrote:  When I tried to do e^(-t)/e^(t) with t being a variable the answer should be 1/e^(2*t) but in the hp prime the answer is 1/e^(t^(2)). But I think it's a visual problem because when I integrate the expression it gives the correct answer.

I have attached an image showing it.
Hi Juan,

it's the same:
1/e^(2*t)=1/e^(t^(2))

I suppose you can 'linearise' like on the 50G but i dont know the keyword on the prime.

EDIT :It's 'lin' (LIN on 50G) and you get e^-(2.t)
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11-11-2014, 11:59 PM (This post was last modified: 11-12-2014 12:13 AM by Han.)
Post: #3
RE: Error with exponential fractions
Perhaps the previous poster (Gilles) meant to write that:
\[ \frac{e^{-t}}{e^{t}} = \left( \frac{1}{e^t}\right)^2 = \frac{1}{\left( e^{t}\right)^2}\]

Indeed, this is what the HP Prime is showing -- except it is missing a pair of necessary outer parentheses.

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11-12-2014, 12:47 AM
Post: #4
RE: Error with exponential fractions
(11-11-2014 08:57 PM)Gilles Wrote:  it's the same:
1/e^(2*t)=1/e^(t^(2))

You are telling us that \(2\cdot t=t^2\)?
Seriously?
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11-12-2014, 01:03 AM
Post: #5
RE: Error with exponential fractions
(11-11-2014 11:59 PM)Han Wrote:  Indeed, this is what the HP Prime is showing -- except it is missing a pair of necessary outer parentheses.

That's not what the HP Prime is showing. Simply put: it shows a wrong result.
Exponentiation is right associative:
\[\frac{1}{e^{t^2}}=\frac{1}{e^{(t^2)}}\]
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11-12-2014, 02:53 AM (This post was last modified: 11-12-2014 03:07 AM by kcnicho.)
Post: #6
RE: Error with exponential fractions
The Primes result is IN ERROR. I did this same calculation on Wolfram Alpha and TI-Nspire, both of which gave correct results.

The Prime is an awesome calculator, the best hardware HP has had in many years. However, if you cannot RELY on it giving CORRECT ANSWERS, which is kinda the whole point of a calculator, then, well, what's the point??? It's fine for a toy, but when you really need the correct answer, stuff like this will make me think twice before using it for anything really important. If there's any doubt in the users mind (and there are many other choices available) they will reach for one of those other devices they have more confidence in.

If you already know the correct answer (at least enough to know the Prime is giving the incorrect answer) then you probably didn't really need the calculator for that problem in the first place. You use a calculator to give you correct answers to stuff you DON'T already know!

I really want to like this calculator. I want to be able to rely on it like I did my HP15C & the many models after that. But the Prime just seems to have these basic problems with its CAS, that I'm wondering whether I can rely on it at all?

Is this a result of HP outsourcing its quality control and error checking to the end users due to the expense of doing it properly in house, and dedicating the required resources?

C'mon folks, lets get with the program. I challenge HP and the Prime Team to make this calculator what it could (should) be; the best, most accurate handheld computing device for mathematics available. Period. We're not going to get there with errors like this!
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11-12-2014, 03:26 AM
Post: #7
RE: Error with exponential fractions
(11-12-2014 01:03 AM)Thomas Klemm Wrote:  
(11-11-2014 11:59 PM)Han Wrote:  Indeed, this is what the HP Prime is showing -- except it is missing a pair of necessary outer parentheses.

That's not what the HP Prime is showing. Simply put: it shows a wrong result.
Exponentiation is right associative:
\[\frac{1}{e^{t^2}}=\frac{1}{e^{(t^2)}}\]

If you type:

\[ simplify\left(\frac{e^{-x}}{e^{x}}\right) \]

and then follow up with:

\[ Ans - \frac{1}{e^{2x}} \]

and then use the simplify menu option, you get the correct result 0. In other words, the HP Prime is calculating it correctly, but displaying it incorrectly due to a missing set of parentheses. I was not suggesting that what it was displaying was correct and simply noting that
\[ \frac{1}{e^{x^2}} \text{ looks like the correct expression} \frac{1}{(e^x)^2} \]
but lacking the the necessary parentheses.

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11-12-2014, 05:06 AM
Post: #8
RE: Error with exponential fractions
It seems that if you copy and past the "e^t^2" from the display back to the enter line, the Prime will put the appropriate parenthesis in place.
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11-12-2014, 06:26 AM
Post: #9
RE: Error with exponential fractions
(11-12-2014 02:53 AM)kcnicho Wrote:  I really want to like this calculator. I want to be able to rely on it like I did my HP15C & the many models after that. But the Prime just seems to have these basic problems with its CAS, that I'm wondering whether I can rely on it at all?
It's not a CAS bug, it's an UI bug as can be seen by unchecking textbook display (2-d display/entry is not as mature as 1-d entry/output).
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11-12-2014, 07:44 AM (This post was last modified: 11-12-2014 08:01 AM by Gilles.)
Post: #10
RE: Error with exponential fractions
(11-12-2014 03:26 AM)Han Wrote:  
(11-12-2014 01:03 AM)Thomas Klemm Wrote:  That's not what the HP Prime is showing. Simply put: it shows a wrong result.
Exponentiation is right associative:
\[\frac{1}{e^{t^2}}=\frac{1}{e^{(t^2)}}\]

If you type:

\[ simplify\left(\frac{e^{-x}}{e^{x}}\right) \]

and then follow up with:

\[ Ans - \frac{1}{e^{2x}} \]

and then use the simplify menu option, you get the correct result 0. In other words, the HP Prime is calculating it correctly, but displaying it incorrectly due to a missing set of parentheses. I was not suggesting that what it was displaying was correct and simply noting that
\[ \frac{1}{e^{x^2}} \text{ looks like the correct expression} \frac{1}{(e^x)^2} \]
but lacking the the necessary parentheses.

Yes... I've miss the parenthesis bug of the Prime in 'textbook' display in my fisrt post. Idea is :
(x^a)^b = x^(a.b) and not that 2.t=t²

2-d display/entry must be improved. It would also be fine if we could manipulate 'algebraic' objects like in the EQW of the 50G (to change a subset of equation, partial simplification or evaluation, to swap elements of the equation etc.)
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11-12-2014, 09:37 AM
Post: #11
RE: Error with exponential fractions
(11-12-2014 06:26 AM)parisse Wrote:  
(11-12-2014 02:53 AM)kcnicho Wrote:  I really want to like this calculator. I want to be able to rely on it like I did my HP15C & the many models after that. But the Prime just seems to have these basic problems with its CAS, that I'm wondering whether I can rely on it at all?
It's not a CAS bug, it's an UI bug as can be seen by unchecking textbook display (2-d display/entry is not as mature as 1-d entry/output).

Hope there is a new firmware soon. Typical and repeated question: Any aproximate date of release?
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11-12-2014, 10:08 AM
Post: #12
RE: Error with exponential fractions
(11-12-2014 02:53 AM)kcnicho Wrote:  The Primes result is IN ERROR. I did this same calculation on Wolfram Alpha and TI-Nspire, both of which gave correct results.

The Prime is an awesome calculator, the best hardware HP has had in many years. However, if you cannot RELY on it giving CORRECT ANSWERS, which is kinda the whole point of a calculator, then, well, what's the point??? It's fine for a toy, but when you really need the correct answer, stuff like this will make me think twice before using it for anything really important. If there's any doubt in the users mind (and there are many other choices available) they will reach for one of those other devices they have more confidence in.

If you already know the correct answer (at least enough to know the Prime is giving the incorrect answer) then you probably didn't really need the calculator for that problem in the first place. You use a calculator to give you correct answers to stuff you DON'T already know!

I really want to like this calculator. I want to be able to rely on it like I did my HP15C & the many models after that. But the Prime just seems to have these basic problems with its CAS, that I'm wondering whether I can rely on it at all?

Is this a result of HP outsourcing its quality control and error checking to the end users due to the expense of doing it properly in house, and dedicating the required resources?

C'mon folks, lets get with the program. I challenge HP and the Prime Team to make this calculator what it could (should) be; the best, most accurate handheld computing device for mathematics available. Period. We're not going to get there with errors like this!

Ah, but does it have the benefit of being a CONSISTENT bug? Compare with the thread: HP 30b: Bug in Student function?
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11-12-2014, 01:45 PM
Post: #13
RE: Error with exponential fractions
(11-12-2014 06:26 AM)parisse Wrote:  
(11-12-2014 02:53 AM)kcnicho Wrote:  I really want to like this calculator. I want to be able to rely on it like I did my HP15C & the many models after that. But the Prime just seems to have these basic problems with its CAS, that I'm wondering whether I can rely on it at all?
It's not a CAS bug, it's an UI bug as can be seen by unchecking textbook display (2-d display/entry is not as mature as 1-d entry/output).

You are probably correct, so I apologize for "blaming the CAS". However, I hope you would agree that the point of my post still reamains. Whether it's the CAS, the display routines, the buttons or the battery that's at fault, what ends up on the display is what counts, and needs to be correct.
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11-12-2014, 03:12 PM
Post: #14
RE: Error with exponential fractions
(11-12-2014 06:26 AM)parisse Wrote:  
(11-12-2014 02:53 AM)kcnicho Wrote:  I really want to like this calculator. I want to be able to rely on it like I did my HP15C & the many models after that. But the Prime just seems to have these basic problems with its CAS, that I'm wondering whether I can rely on it at all?
It's not a CAS bug, it's an UI bug as can be seen by unchecking textbook display (2-d display/entry is not as mature as 1-d entry/output).

As it's merely a UI bug I guess it'll be fixed immediately - or perhaps not?
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11-12-2014, 06:01 PM (This post was last modified: 11-12-2014 10:11 PM by Tim Wessman.)
Post: #15
RE: Error with exponential fractions
Technically, it is not an issue because what is being used is the "square" operator which has traditionally in algebraic entry calcs had a DIFFERENT evaluation priority then power. That is why it is the small superscript 2 instead of a normal sized ^2. I never liked it, but when the 39gII was made we were directed to follow that convention.

However, I agree it is not good and hope I can resolve it before too long.

[edit]
I assume this is more what you are looking for?

[Image: new_exp.png]

TW

Although I work for the HP calculator group, the views and opinions I post here are my own.
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11-13-2014, 01:06 AM (This post was last modified: 11-13-2014 01:21 AM by Thomas Klemm.)
Post: #16
RE: Error with exponential fractions
(11-12-2014 06:01 PM)Tim Wessman Wrote:  the "square" operator which has traditionally in algebraic entry calcs had a DIFFERENT evaluation priority then power.

This sure is related to the precedence of implied uglification or maybe even imaginary numbers. You know eleventeen, thirty-twelve, and all those. It's a little confusing at first.

Cheers
Thomas
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