4
$\begingroup$

I have a function defined as

a[x_]:=If[x==0,const,f[x]]

where $f(0)\neq const$.

How do I evaluate $a(x)$ such that I just get $f(x)$ without having to put in a specific x value greater than 0? I've tried things like $/;$, Assumptions and Assuming, but haven't been able to do it. This seems like it should be a simple thing, any ideas?

Improve this question
$\endgroup$
1
  • 1
    $\begingroup$ This answer sheds some light on why this might not be as simply as it first seems. $\endgroup$ – Quantum_Oli Jun 8 '17 at 16:00
2
$\begingroup$

You can use TrueQ:

a[x_] := If[TrueQ[x == 0], const, f[x]]

Or the fourth parameter of If:

a[x_] := If[x == 0, const, f[x], f[x]]

Or formulate your function in two definitions:

a[x_] /; x == 0 = const;
a[x_] := f[x]

Recommended reading:

Improve this answer
$\endgroup$
2
  • $\begingroup$ Or If[x === 0, ...] which is what I usually do. $\endgroup$ – Carl Woll Jun 8 '17 at 16:13
  • 1
    $\begingroup$ @CarlWoll ...and what I expressly warn about in the final link in my answer ;^) $\endgroup$ – Mr.Wizard Jun 8 '17 at 16:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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