[CAS] find domain for function?

09162015, 10:46 AM
Post: #1




[CAS] find domain for function?
Hello,
is there a function / command to find the domain, for whitch a function is defined? Examples: f(x) = x/(x1) should result in x<>1 f(x) = ln(x) should result in x > 0 regards Wolfgang 

09182015, 01:20 PM
Post: #2




RE: [CAS] find domain for function?
Just bring it on top again!
@parisse: Is there no such command? regards Wolfgang 

09182015, 01:42 PM
(This post was last modified: 09182015 01:44 PM by Tim Wessman.)
Post: #3




RE: [CAS] find domain for function?
There is not. He feels it is not a useful thing to have.
TW Although I work for the HP calculator group, the views and opinions I post here are my own. 

09182015, 02:10 PM
Post: #4




RE: [CAS] find domain for function?
A graph would serve the same purpose as such a command, and would be more useful from a pedagogical point of view.
Graph 3D  QPI  SolveSys 

09182015, 02:11 PM
(This post was last modified: 09182015 02:14 PM by Helge Gabert.)
Post: #5




RE: [CAS] find domain for function?
BTW, The 50G has TABVAR, which returns the domain and poles for some functions (reducible to a rational expression), but I never found that particularly useful either. Easier to just graph the function!


09182015, 03:37 PM
Post: #6




RE: [CAS] find domain for function?
Xcas has the singular function, it does not return exactly the domain (for example singular(ln(x)) returns [0]), but it gives some informations about.


09192015, 08:23 AM
Post: #7




RE: [CAS] find domain for function?
As for polynomials functions there is no problem, their domain is R.
For fractional functions 1/f(x) we can solve f(x)=0 and the roots are the ones to be excluded from R. For irrational functions sqrt(f(x)), solving f(x)>=0 is enough. In many cases in order to find the domain of a function we need to set a system: y=sqrt(log(x^28*x+8)), solve({x^28*x+8>0,log(x^28*x+8)>=0}) and that's all !!! Domain found !!!!! Algebraically, not graphically B) ^_^ Best, Aries ;) 

11132019, 09:49 AM
Post: #8




RE: [CAS] find domain for function?
Perhaps with past release of firmware, it could not do so.
With the latest release (2018 10 16), I found domain command which can be used to find domain: For example, to find domain of f(x) = 1/(x1), simply use: domain(1/(x1),x) it will return x<>1 I'm just thinking howto find range of this function. Perhaps the following command can help: domain(solve(y=1/(x1),x),y) it will return y<>0 

11142019, 09:00 AM
Post: #9




RE: [CAS] find domain for function?
Not all functions are invertible in their domain, y=x^2 is noninvertible in its domain.
What if f(x) is noninvertible ? A function f is invertible if and only if it's injective, that is whenever f(x)=f(y), x=y. In certain cases restricting domain of f(x) could make it invertible. Best, Aries 

11142019, 11:20 AM
Post: #10




RE: [CAS] find domain for function?
@ Aries
You can use domain(solve(y=x^2,x),y). The calculator will give result y>=0 However, this may not work with implicit function e.g abs(x) + abs(y) = 4 

11152019, 01:34 AM
Post: #11




RE: [CAS] find domain for function?  
11152019, 09:43 AM
Post: #12




RE: [CAS] find domain for function?
As for the image (range) of f it's supposed to work with implicit functions as well but I suggest drawing a sketch or looking for maximum and minimum of y or even analysing f.
Best, Aries 

11182019, 06:06 AM
Post: #13




RE: [CAS] find domain for function?
hello,
Doesn't tabvar solve your problem? Cyrille Although I work for the HP calculator group, the views and opinions I post here are my own. I do not speak for HP. 

11182019, 12:13 PM
Post: #14




RE: [CAS] find domain for function?
Well, of course it does
Best, Aries 

11202019, 04:01 AM
Post: #15




RE: [CAS] find domain for function?
tabvar is one of my favorite items on the HP 50g, and on the Prime!


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