[CAS] Potential Bug with given (|). [SOLVED]

[CH3791]

Good evening/morning to the good folk at HP,
For some maths questions, I have to restrict the domain. So I use the given symbol (|) in CAS. I would have something like:
solve(x^2-8=0,x)|(x>0)
That works perfectly.

But when I add another condition like so:
solve(x^2-8=0,x)|((x>0) AND (x<10))
The calculator creates a CAS variable called x, in the form of a matrix. And from this point on, the variable x will always have the "temporary" domain imposed onto it.
solve(x^2-8=0,x) will start to return 2*root(2) only.
solve(x+3=0,x) will give [].
and so on.

Unless this is an actual feature, can you guys fix this bug ASAP. Because I can already imagine how dangerous this would be for examinations...

[Mark Hardman]

This would appear to be by design. The CAS system is converting the compound given statement into the following explicit assumptions:

assume(x>0) -> x
additionally(x<10) -> x

This creates the following permanent assumptions on x:

about(x) -> assume[[],[line[0,10]],[0,10]]

Which provides the correct solution:

solve((x^2-8) = 0,x) -> {2*√2}

To avoid future use of the assumptions on x, they must be purged:

purge(x) -> assume[[],[line[0,10]],[0,10]]
about(x) -> x

Mark Hardman

[Nigel (UK)]

(10-30-2016 05:03 PM)Mark Hardman Wrote:  This would appear to be by design. The CAS system is converting the compound given statement into the following explicit assumptions:

assume(x>0) -> x
additionally(x<10) -> x

This creates the following permanent assumptions on x:

about(x) -> assume[[],[line[0,10]],[0,10]]

Which provides the correct solution:

solve((x^2-8) = 0,x) -> {2*√2}

To avoid future use of the assumptions on x, they must be purged:

purge(x) -> assume[[],[line[0,10]],[0,10]]
about(x) -> x

Mark Hardman

If this is intentional I think it is a bad idea. I think of the "|" operator as making a temporary assignment to a variable or applying a temporary restriction and I suspect that most people would feel this way too.

TI CAS calculators have got a menu function that clears single-character variable names (a-z). It would be a good idea to advise users to implement their own such function on the Prime, and to use it regularly! Thanks to CH3791 for pointing out this potential pitfall.

Nigel (UK)

[parisse]

Well spotted, I'm fixing that in giac source.

[CH3791]

Wow... guys... Seeing this genuinely put a smile onto my face. Time and time again, you have read over my queries (no matter how stupid they may be), and within a day have come up with an awesome response! For me as a highschool student, it was quite a gamble to move from the Casio Classpad to this mysterious, high-powered machine, but so far everything has played out flawlessly.

Part of that of course, is due to the hospitality of this community and I can't thank you guys enough for that.

[compsystems]

Alphabetic variables capitalized does not work.

solve(X^2-8 = 0,X) | X>0 AND X<10; [enter] {-2*√(2),2*√(2)}
about(X); [enter] 0

now

x:=foo; [enter] ...
solve(x^2-8 = 0,x) | x>0 AND x<10; [enter] {2*√(2)} // This should display a message that says the "contents of the variable x will be deleted" [yes/no] or "error x is not empty" otherwise, it causes of data loss or overwriting
x; [enter] x =(