|Re: HP Prime: Proper Use of Home View and CAS View|
Message #4 Posted by Joe Horn on 4 Dec 2013, 8:52 p.m.,
in response to message #3 by James Williams
I'm not a design team member, or even an HP employee, but I think I understand the concept behind Home versus CAS.
I was hoping for some members of the HP design team to weigh in here on what their use cases were for when to use Home View and when to use CAS View. Understanding that will help make me more proficient on this calculator.
HP Prime Home is like Approx mode on the HP 50g.
HP Prime CAS is like Exact mode on the HP 50g.
For those without 50g experience:
Home is primarily for approximate numeric calculations.
CAS is primarily for exact symbolic operations.
Simple example: A student is asked, "What is the square root of 12?" Should the student answer "Approximately 3.46410161514", or "Exactly 2 times the square root of 3"? Both answers are correct, and both are needed in different circumstances. That's why Prime offers both environments.
Another simple example: What is 2^1234? Home says it's approximately 2.958 times 10^371. That's plenty good enough for most real-world purposes. But if you ever need every digit of the exact answer (e.g. for Number Theory work), CAS returns all 372 digits of 2^1234. Whichever you need, Prime offers both.
I hope that this distinction clarifies why both modes exist, and why SIN(pi) (in radian mode) gets different results in Home and CAS.
Even 0.5-0.4-0.1 gets different results in Home and CAS. And it's not a bug. Nor is it a surprise to anyone who understands the difference in purpose and implementation of Home and CAS. It's only a surprise (and an annoyance) to those who expect Home and CAS to work the same. (If they worked the same, there would be no need for both to exist).
Hope that helped! Or at least I hope that it didn't make it worse.
"Everything above may be wrong." -- Richard Bach ("Illusions")
Edit: Oops, I even got that quote wrong. It's "Everything in this book may be wrong." *sigh*
Edited: 4 Dec 2013, 9:00 p.m.