class ROOT::Math::PtEtaPhiM4D<Double32_t>

      Set internal data based on an array of 4 Scalar numbers

      get internal data into an array of 4 Scalar numbers

      Set internal data based on 4 Scalar numbers

      get internal data into 4 Scalar numbers

 --------- Coordinates and Coordinate-like Scalar properties -------------
 4-D Cylindrical eta coordinate accessors

       M() is the invariant mass;
       in this coordinate system it can be negagative if set that way.

 other coordinate representation

       magnitude of momentum

       squared magnitude of spatial components (momentum squared)

       energy squared

       Energy (timelike component of momentum-energy 4-vector)

      vector magnitude squared (or mass squared)
      In case of negative mass (spacelike particles return negative values)

       transverse spatial component squared

       transverse mass squared

      transverse mass - will be negative if Mt2() is negative

       transverse energy squared

      transverse energy

 restrict the value of negative mass to avoid unphysical negative E2 values
 M2 must be less than P2 for the tachionic particles - otherwise use positive values

      polar angle

 --------- Set Coordinates of this system  ---------------

      set Pt value

      set eta value

      set phi value

      set M value

       set values using cartesian coordinate system

 ------ Manipulations -------------

      negate the 4-vector -- Note that the energy cannot be negate (would need an additional data member)
      therefore negate will work only on the spatial components
      One would need to use negate only with vectors having the energy as data members

      Scale coordinate values by a scalar quantity a

 ============= Compatibility secition ==================
 The following make this coordinate system look enough like a CLHEP
 vector that an assignment member template can work with either

 ====== Set member functions for coordinates in other systems =======