Class describing a cylindrical coordinate system based on rho, z and phi.
      The base coordinates are rho (transverse component) , z and phi
      Phi is restricted to be in the range [-PI,PI)
      @ingroup GenVector

      Set internal data based on an array of 3 Scalar numbers ( rho, z , phi)
      get internal data into an array of 3 Scalar numbers ( rho, z , phi)
      Set internal data based on 3 Scalar numbers ( rho, z , phi)
      get internal data into 3 Scalar numbers ( rho, z , phi)
 setters (only for data members)
       set the rho coordinate value keeping z and phi constant
       set all values using cartesian coordinates
      Exact component-by-component equality
============= 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 =======