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For a fake function like:

fun[x_] := x^0/x!;

and list:

list={0,0,0.1,0.2,0.9,0.8,0,0};

It will get error in this way cause the 0^0 is indeterminate:

fun[list]

In that case,I want to just leave the 0 element in the list as it is and only calculate the element that larger than 0. Are there some easy and fast way to implement this?

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    $\begingroup$ fun[x_?Positive] := x^0/x!;fun[0]=0; $\endgroup$
    – Alan
    Commented May 21, 2018 at 16:29
  • $\begingroup$ fun[x_] := x^0/x! /; x > 0 fun[0] = 0; fun /@ list $\endgroup$
    – Fraccalo
    Commented May 21, 2018 at 16:31

1 Answer 1

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You can define a special case for the $0$ input. 

ClearAll[fun]
fun[0] = 0
fun[x_] := x^0/x!
SetAttributes[fun, Listable]

fun[list]

(* Out: {0, 0, 1.05114, 1.08912, 1.03975, 1.07367, 0, 0} *)

Notice that you can use your original function on a list directly (i.e. fun[list] instead of mapping it over a list as in fun /@ list), because you take advantage of the Listable attributes of the operations used in your function.

If you define the special case for $0$ input, however, it is easiest to make your function explicitly Listable so that it itself automatically threads over lists and the $0$ special case fires appropriately.

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  • $\begingroup$ Thank you for the detailed answer! $\endgroup$
    – cj9435042
    Commented May 21, 2018 at 16:42

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