I need to define a function that takes an input and if and only if its a positive real, outputs the input. If not, the output should be 0. The input could be complex valued or indeterminate.
Heres what I defined;
myMax[x_] :=
Module[{},
If[x === Indeterminate, 0, If[Element[x, Reals], Max[0, x], 0]]];
This function is not compilable efficiently in mathematica. Is it possible to define such a function using just compilable functions?
Not sure if this is the most efficient way, but it should work as expected and is also compilable:
If[Re[x] > 0 && Im[x] == 0, x, 0]
Note that Indeterminate is a Mathematica construct and cannot be used inside a compilable function without reverting back to the main kernel. For example, see the error messages if you do:
Compile[{x, y}, x/y][0, 0]
(*Indeterminate*)
CompiledFunction::cfne: Numerical error encountered; proceeding with uncompiled evaluation.
Power::infy: Infinite expression 1/0. encountered.
Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered.
Therefore, if you expect that Indeterminate could happen in your code, it is best to check the values of arguments before executing a possibly dangerous operation, for example (giving 0 for problematic numbers as in your case):
Compile[{x, y}, If[y == 0, 0, x/y]][0, 0]
(* 0. *)
myMax = Compile[{{x, _Complex}}, If[Im@x==0, Max[Re@x, 0], 0]]? $\endgroup$