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+--- Thread: How to simplify result from domain function (/thread-14594.html)
How to simplify result from domain function - teerasak - 03-02-2020 07:58 AM
I use domain() function to find the domain of function Sqrt(x^2-9)/(x-3)
The calculator returns result [x<=-3 x>=3 and x <>3]
When simplify, it is expected to have [x<=-3 x>3], but the calculator returns result [x<=-3 x>=3]
![[Image: pic1.png]](https://i.ibb.co/CBBwh70/pic1.png)
How can we have correct simplified answer?
RE: How to simplify result from domain function - Albert Chan - 03-02-2020 12:47 PM
The bug probably not from simplify, but x≠3
XCas> purge(x)
XCas> x >= 3 // returns x ≥ 3, as expected
XCas> x != 3 // returns true ???
XCas> [(x <= -3), (x >= 3) and (x != 3)] // dropped "and true", returns [x <= -3, x >= 3]
RE: How to simplify result from domain function - parisse - 03-02-2020 01:18 PM
It's unfortunately unavoidable. x!=3 will return true, because in this test x is considered to be a variable, and a variable is not the same as an integer.
RE: How to simplify result from domain function - teerasak - 03-03-2020 05:46 AM
I see. So the calculator treats x>=3, x<>3 as logical comparison rather than a set of number.
Any representation of the set x>=3?
RE: How to simplify result from domain function - parisse - 03-03-2020 06:06 AM
There is an internal representation, used by assume/about, but no user commands.
RE: How to simplify result from domain function - compsystems - 03-03-2020 05:18 PM
A new command to graph interval is very important, for example to graph the solution [x≤-3, (x≥3) AND (x≠3)] the following instruction is required
F1(X):=PIECEWISE( X≤-3, 0, (X≥3) AND (X≠3), 0 ) [enter] [plot]
RE: How to simplify result from domain function - CyberAngel - 03-03-2020 08:55 PM
(03-03-2020 06:06 AM)parisse Wrote: There is an internal representation, used by assume/about, but no user commands.
Any way of adding an exported command or function?
Would it be useful in the described cases?
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RE: How to simplify result from domain function - parisse - 03-04-2020 08:10 PM
No, there is no support for the internal representation of assume in user commands.
RE: How to simplify result from domain function - CyberAngel - 03-04-2020 09:02 PM
(03-04-2020 08:10 PM)parisse Wrote: No, there is no support for the internal representation of assume in user commands.
I know there isn't at the moment
but
would it be useful
if you would ADD such a support?
Is it possible to add new keywords?
like this: "set { x<3 x>3 }"
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RE: How to simplify result from domain function - parisse - 03-05-2020 06:31 AM
There is nothing planned. I have myself no idea how to handle properly these kinds of objects.
RE: How to simplify result from domain function - CyberAngel - 03-05-2020 07:54 AM
(03-05-2020 06:31 AM)parisse Wrote: There is nothing planned. I have myself no idea how to handle properly these kinds of objects.
okay
Users just have to careful and
also know – not just the math
but also the limitations of their tools.
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