Class describing a polar 2D coordinate system based on r and phi
       Phi is restricted to be in the range [-PI,PI)
       @ingroup GenVector

      Set internal data based on 2 Scalar numbers
      get internal data into 2 Scalar numbers
 setters (only for data members)
       set the r coordinate value keeping phi constant
       set all values using cartesian coordinates
============= Compatibility section ================== The following make this coordinate system look enough like a CLHEP vector that an assignment member template can work with either
{ return X();}============= Specializations for improved speed ================== (none) ====== Set member functions for coordinates in other systems =======