[CAS] find domain for function? - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html) +--- Forum: HP Prime (/forum-5.html) +--- Thread: [CAS] find domain for function? (/thread-4727.html) |
[CAS] find domain for function? - ww63 - 09-16-2015 10:46 AM Hello, is there a function / command to find the domain, for whitch a function is defined? Examples: f(x) = x/(x-1) should result in x<>1 f(x) = ln(x) should result in x > 0 regards Wolfgang RE: [CAS] find domain for function? - ww63 - 09-18-2015 01:20 PM Just bring it on top again! @parisse: Is there no such command? regards Wolfgang RE: [CAS] find domain for function? - Tim Wessman - 09-18-2015 01:42 PM There is not. He feels it is not a useful thing to have. RE: [CAS] find domain for function? - Han - 09-18-2015 02:10 PM A graph would serve the same purpose as such a command, and would be more useful from a pedagogical point of view. RE: [CAS] find domain for function? - Helge Gabert - 09-18-2015 02:11 PM 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! RE: [CAS] find domain for function? - parisse - 09-18-2015 03:37 PM 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. RE: [CAS] find domain for function? - Aries - 09-19-2015 08:23 AM 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^2-8*x+8)), solve({x^2-8*x+8>0,log(x^2-8*x+8)>=0}) and that's all !!! Domain found !!!!! Algebraically, not graphically B-) ^_^ Best, Aries ;-) RE: [CAS] find domain for function? - teerasak - 11-13-2019 09:49 AM 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/(x-1), simply use: domain(1/(x-1),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/(x-1),x),y) it will return y<>0 RE: [CAS] find domain for function? - Aries - 11-14-2019 09:00 AM Not all functions are invertible in their domain, y=x^2 is non-invertible in its domain. What if f(x) is non-invertible ? 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 RE: [CAS] find domain for function? - teerasak - 11-14-2019 11:20 AM @ 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 RE: [CAS] find domain for function? - CyberAngel - 11-15-2019 01:34 AM (11-14-2019 11:20 AM)teerasak Wrote: @ Aries Would it help to set: assume(x>=0) assume(y>=0) RE: [CAS] find domain for function? - Aries - 11-15-2019 09:43 AM 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 RE: [CAS] find domain for function? - cyrille de brébisson - 11-18-2019 06:06 AM hello, Doesn't tabvar solve your problem? Cyrille RE: [CAS] find domain for function? - Aries - 11-18-2019 12:13 PM Well, of course it does Best, Aries RE: [CAS] find domain for function? - lrdheat - 11-20-2019 04:01 AM tabvar is one of my favorite items on the HP 50g, and on the Prime! |