Should I replace my TI-89 Swiss Army Knife on the table with the HP Prime?

[Nigel (UK)]

(07-26-2022 05:36 AM)Tom Flatterhand Wrote:  @ijabbott: Thanks for this info!

@Nigel: This is exactly the information that interests me. Especially the trustworthiness of the calculator is important for me. Since I'm not a mathematician and I'm not good at math, I use the TI-89, or now the HP Prime, as my personal mathematician, which helps me, for example, to solve or check my children's math problems. But even when I am dealing with mathematical problems myself, I need a trustworthy instance to test my thoughts. It is important that I can trust the results of the calculator.

>It isn't bug-free, and it looks now as though existing bugs may never be fixed

Can you give me an example?

Here's a couple.

(1) In Home mode, try 10.1^600/10.1^599. The correct answer is 10.1, but the calculator returns 1. Both numerator and denominator overflow and evaluate to 9.99999999999e499. This caught me out a few times with expressions that included factorials of large numbers not throwing an error, but evaluating to an incorrect answer. I think others have noticed this too. In CAS mode there's no problem - both top and bottom evaluate to \(\infty\) and the result is undefined.

(2) Go to CAS mode, and assign 10 to x. solve(x*3/2=3, x) and solve(x*3/2=3., x) return {2} and {2.} respectively. No problem. (Decimal numbers are approximate, just as on the TI.)

Now try solve(x^(3/2)=3, x) and solve(x^(3/2)=3.,x). The first returns {\(9^{1/3}\)}, which is fine, but the second returns {0.94868...}, which is wrong. If x is purged first (purge(x)) then the correct answer is given. So it's sometimes necessary to purge x before solving, and sometimes not. But instead of an error an incorrect answer is silently given.

I'm using software version 20210505. My Windows emulator has version 20210609 and has the same problems; it says that no update is available, so I'm assuming that there is no fix out there.

Nigel (UK)