class HistogramManager

                       Event and Track classes


  The Event class is a naive/simple example of an event structure.
     public:
        char           fType[20];
        char          *fEventName;         //run+event number in character format
        Int_t          fNtrack;
        Int_t          fNseg;
        Int_t          fNvertex;
        UInt_t         fFlag;
        Double32_t     fTemperature;
        Int_t          fMeasures[10];
        Double32_t     fMatrix[4][4];
        Double32_t    *fClosestDistance; //[fNvertex] indexed array!
        EventHeader    fEvtHdr;
        TClonesArray  *fTracks;
        TRefArray     *fHighPt;            //array of High Pt tracks only
        TRefArray     *fMuons;             //array of Muon tracks only
        TRef           fLastTrack;         //pointer to last track
        TRef           fHistoWeb;          //EXEC:GetHistoWeb reference to an histogram in a TWebFile
        TH1F          *fH;
        TBits          fTriggerBits;       //Bits triggered by this event.

   The EventHeader class has 3 data members (integers):
     public:
        Int_t          fEvtNum;
        Int_t          fRun;
        Int_t          fDate;


   The Event data member fTracks is a pointer to a TClonesArray.
   It is an array of a variable number of tracks per event.
   Each element of the array is an object of class Track with the members:
     private:
        Float_t      fPx;           //X component of the momentum
        Float_t      fPy;           //Y component of the momentum
        Float_t      fPz;           //Z component of the momentum
        Float_t      fRandom;       //A random track quantity
        Float_t      fMass2;        //The mass square of this particle
        Float_t      fBx;           //X intercept at the vertex
        Float_t      fBy;           //Y intercept at the vertex
        Float_t      fMeanCharge;   //Mean charge deposition of all hits of this track
        Float_t      fXfirst;       //X coordinate of the first point
        Float_t      fXlast;        //X coordinate of the last point
        Float_t      fYfirst;       //Y coordinate of the first point
        Float_t      fYlast;        //Y coordinate of the last point
        Float_t      fZfirst;       //Z coordinate of the first point
        Float_t      fZlast;        //Z coordinate of the last point
        Double32_t   fCharge;       //Charge of this track
        Double32_t   fVertex[3];    //Track vertex position
        Int_t        fNpoint;       //Number of points for this track
        Short_t      fValid;        //Validity criterion
        Int_t        fNsp;          //Number of points for this track with a special value
        Double32_t  *fPointValue;   //[fNsp] a special quantity for some point.
        TBits        fTriggerBits;  //Bits triggered by this track.

   An example of a batch program to use the Event/Track classes is given
   in this directory: MainEvent.
   Look also in the same directory at the following macros:
     - eventa.C  an example how to read the tree
     - eventb.C  how to read events conditionally

   During the processing of the event (optionally) also a large number
   of histograms can be filled. The creation and handling of the
   histograms is taken care of by the HistogramManager class.