BeginPackage["Normalize`"]

Normalize::usage = "
   Normalize[x] returns a unit vector parallel to x,\n
   which should have head List.  If x=0 it returns Null.\n
   Normalize[x,r] returns a vector of length r parallel to x."

Begin["`private`"]

Normalize::zero = "Cannot normalize ``"

Normalize[x_List] := Message[Normalize::zero,Null] /; x.Conjugate[x]==0
Normalize[x_List] := x/Sqrt[x.Conjugate[x]]
Normalize[x_List,r_] := r Normalize[x]

End[]
EndPackage[]