Hello Group:

This works: (* directly from the help page *)

DensityPlot[Arg[Sqrt[x + I y]], {x, -3, 3}, {y, -3, 3} ]

I want to define the inner function myself with:

f[a_, b_] := a + I b

(* this forum software is removing the underscore in the functions definition ?!?!?..should be f[Placeholder[a], Placeholder[b]]:=a+ I b *)

But then this does not work:

DensityPlot[Arg[Sqrt[f]], {x, -3, 3}, {y, -3, 3} ]

Neither does any of these:

DensityPlot[Evaluate[Arg[Sqrt[f]]], {x, -3, 3}, {y, -3, 3} ]

DensityPlot[Arg[Sqrt[f]], {a, -3, 3}, {b, -3, 3} ]

DensityPlot[Evaluate[Arg[Sqrt[(#1 + I #2) &]]], {x, -3, 3}, {y, -3, 3}]

I have been confused in the past to know when Evaluate[] was needed. It usually fixes these wierd cases.

Thanks in advance.