1
$\begingroup$

I tried it liek this:

My test-function:

fuu[x_] := Expand[FullSimplify[1/x]]

how i find the domain:

domain[f_] := 
 Module[{}, 
  Reduce[Exists[{y}, Element[x, Reals] && y == f, Element[y, Reals]]]]
domain[fuu[x]]
(*x < 0 || x > 0*)

How i tried to find the gaps:

gaps[f_] := 
 Not[Reduce[
   Exists[{y}, Element[x, Reals] && y == f, Element[y, Reals]]]] 
gaps[fuu[x]]
(*! (x < 0 || x > 0)*)

How can i do it that he just says x == 0 ?

$\endgroup$
5
  • $\begingroup$ In v10: FunctionDomain[1/x, x, Reals] // FullSimplify (* x != 0 *) $\endgroup$
    – kirma
    Jun 9, 2015 at 13:50
  • $\begingroup$ I have Mathematica 9.. $\endgroup$
    – baloo
    Jun 9, 2015 at 13:53
  • 1
    $\begingroup$ lol i just needed to Fullsimplify the last one.. $\endgroup$
    – baloo
    Jun 9, 2015 at 13:56
  • 2
    $\begingroup$ sudo, rather than adding the answer to your question, would you mind posting it as an actual answer and in due time accepting it? That would make the question show up as answered, and it is encouraged on stackexchange to answer your own questions when you can. $\endgroup$
    – MarcoB
    Jun 9, 2015 at 14:00
  • $\begingroup$ @MarcoB thanks for taking the time to explain.. I am willing to learn :q $\endgroup$
    – baloo
    Jun 9, 2015 at 14:06

1 Answer 1

1
$\begingroup$
gaps[f_] := 
     Not[Reduce[
       Exists[{y}, Element[x, Reals] && y == f, Element[y, Reals]]]] 
    gaps[fuu[x]] // FullSimplify
    (*x == 0*)
$\endgroup$
2
  • $\begingroup$ now i feel stupid and smart at the same moment :3 lol $\endgroup$
    – baloo
    Jun 9, 2015 at 14:02
  • $\begingroup$ Thanks for posting the answer (+1) And hey, you solved your problem, nothing to feel stupid about there! :-) $\endgroup$
    – MarcoB
    Jun 9, 2015 at 14:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.