TTree

class TTree : public TNamed, public TAttLine, public TAttFill, public TAttMarker

    protected:

      const Text_t* GetNameByIndex(TString& varexp, Int_t* index, Int_t colindex)
      virtual Int_t MakeChopt(Option_t* option)
      virtual Int_t MakeFitOptions(Option_t* option)
       virtual void MakeIndex(TString& varexp, Int_t* index)
       virtual void SetDirectory(TDirectory* dir)
               void TakeAction(Int_t nfill, Int_t& npoints, Int_t& action, TObject* obj, Option_t* option)
               void TakeEstimate(Int_t nfill, Int_t& npoints, Int_t action, TObject* obj, Option_t* option)

    public:

                   TTree TTree()
                   TTree TTree(Text_t* name, Text_t* title, Int_t maxvirtualsize = 0)
                   TTree TTree(TTree&)
            virtual void ~TTree()
            virtual void AddTotBytes(Int_t tot)
            virtual void AddZipBytes(Int_t zip)
            virtual void AutoSave()
                TBranch* Branch(Text_t* name, void* clonesaddress, Int_t bufsize = 32000, Int_t splitlevel = 1)
                TBranch* Branch(Text_t* name, Text_t* classname, void* addobj, Int_t bufsize = 32000, Int_t splitlevel = 1)
                TBranch* Branch(Text_t* name, void* address, Text_t* leaflist, Int_t bufsize = 32000)
            virtual void Browse(TBrowser* b)
            virtual void BuildIndex(char* majorname, char* minorname)
                 TClass* Class()
            virtual void ClearFormula()
          virtual TTree* CloneTree(Int_t nentries = -1)
            virtual void CompileVariables(Text_t* varexp, Text_t* selection)
           virtual Int_t CopyEntries(TTree* tree, Int_t nentries = -1)
            virtual void CreatePacketGenerator(Int_t nentries, Stat_t firstEntry)
            virtual void Draw(Option_t* opt)
            virtual void Draw(TCut varexp, TCut selection, Option_t* option, Int_t nentries = 1000000000, Int_t firstentry = 0)
            virtual void Draw(Text_t* varexp, Text_t* selection, Option_t* option, Int_t nentries = 1000000000, Int_t firstentry = 0)
                    void DropBuffers(Int_t nbytes)
            virtual void EntryLoop(Int_t& action, TObject* obj, Int_t nentries = 1000000000, Int_t firstentry = 0, Option_t* option)
            virtual void EstimateLimits(Int_t estimate, Int_t nentries = 1000000000, Int_t firstentry = 0)
           virtual Int_t Fill()
                    void FindGoodLimits(Int_t nbins, Int_t& newbins, Float_t& xmin, Float_t& xmax)
            virtual void Fit(Text_t* formula, Text_t* varexp, Text_t* selection, Option_t* option, Option_t* goption, Int_t nentries = 1000000000, Int_t firstentry = 0)
        virtual TBranch* GetBranch(Text_t* name)
           virtual Int_t GetChainOffset()
                  TFile* GetCurrentFile()
             TDirectory* GetDirectory()
          virtual Stat_t GetEntries()
           virtual Int_t GetEntry(Int_t entry = 0, Int_t getall = 0)
           virtual Int_t GetEntryNumber(Int_t entry)
           virtual Int_t GetEntryNumberWithIndex(Int_t major, Int_t minor)
           virtual Int_t GetEntryWithIndex(Int_t major, Int_t minor)
           virtual Int_t GetEstimate()
                   Int_t GetEvent(Int_t entry = 0, Int_t getall = 0)
             TEventList* GetEventList()
       virtual Double_t* GetIndex()
          virtual TLeaf* GetLeaf(Text_t* name)
          virtual TList* GetListOfActiveBranches()
      virtual TObjArray* GetListOfBranches()
      virtual TObjArray* GetListOfLeaves()
           virtual Int_t GetMaxEntryLoop()
         virtual Float_t GetMaximum(Text_t* columname)
           virtual Int_t GetMaxVirtualSize()
         virtual Float_t GetMinimum(Text_t* columname)
           TTreeFormula* GetMultiplicity()
           virtual Int_t GetNbranches()
            virtual void GetNextPacket(TSlave* sl, Int_t& nentries, Stat_t& firstentry, Stat_t& processed)
       TPacketGenerator* GetPacketGenerator()
           virtual Int_t GetPacketSize()
           virtual Int_t GetReadEntry()
           virtual Int_t GetReadEvent()
           virtual Int_t GetScanField()
           TTreeFormula* GetSelect()
           virtual Int_t GetSelectedRows()
              TSelector* GetSelector()
          virtual Stat_t GetTotBytes()
        virtual Float_t* GetV1()
        virtual Float_t* GetV2()
        virtual Float_t* GetV3()
           TTreeFormula* GetVar1()
           TTreeFormula* GetVar2()
           TTreeFormula* GetVar3()
           TTreeFormula* GetVar4()
       virtual Double_t* GetW()
          virtual Stat_t GetZipBytes()
            virtual void IncrementTotalBuffers(Int_t nbytes)
         virtual TClass* IsA()
          virtual Bool_t IsFolder()
           virtual Int_t LoadTree(Int_t entry)
            virtual void Loop(Option_t* option, Int_t nentries = 1000000000, Int_t firstentry = 0)
           virtual Int_t MakeClass(char* classname = 0)
           virtual Int_t MakeCode(char* filename = 0)
                  Bool_t MemoryFull(Int_t nbytes)
            virtual void Print(Option_t* option)
            virtual void Project(Text_t* hname, Text_t* varexp, Text_t* selection, Option_t* option, Int_t nentries = 1000000000, Int_t firstentry = 0)
            virtual void Reset(Option_t* option)
            virtual void Scan(Text_t* varexp, Text_t* selection, Option_t* option, Int_t nentries = 1000000000, Int_t firstentry = 0)
            virtual void SetAutoSave(Int_t autosave = 10000000)
            virtual void SetBranchAddress(Text_t* bname, void* add)
            virtual void SetBranchStatus(Text_t* bname, Bool_t status = 1)
            virtual void SetChainOffset(Int_t offset = 0)
            virtual void SetEstimate(Int_t nentries = 10000)
            virtual void SetEventList(TEventList* list)
            virtual void SetMaxEntryLoop(Int_t maxev = 1000000000)
            virtual void SetMaxVirtualSize(Int_t size = 0)
            virtual void SetName(Text_t* name)
            virtual void SetPacketSize(Int_t size = 100)
            virtual void SetScanField(Int_t n = 50)
            virtual void SetSelector(TSelector* selector = 0)
            virtual void SetSelector(Text_t* macroname)
            virtual void SetTimerInterval(Int_t msec = 333)
            virtual void SetUpdate(Int_t freq = 0)
            virtual void Show(Int_t entry = -1)
            virtual void ShowMembers(TMemberInspector& insp, char* parent)
            virtual void StartViewer(Int_t ww = 520, Int_t wh = 400)
            virtual void Streamer(TBuffer& b)
            virtual void UpdateActiveBranches()

  Data Members

    protected:

                  Int_t fScanField       Number of runs before prompting in Scan
                  Int_t fDraw            Last entry loop number when object was drawn
                  Int_t fUpdate          Update frequency for EntryLoop
                  Int_t fMaxEntryLoop    Maximum number of entries to process
                  Int_t fMaxVirtualSize  Maximum total size of buffers kept in memory
                  Int_t fAutoSave        Autosave tree when fAutoSave bytes produced
                 Stat_t fEntries         Number of entries
                 Stat_t fTotBytes        Total number of bytes in all branches before compression
                 Stat_t fZipBytes        Total number of bytes in all branches after compression
                 Stat_t fSavedBytes      Number of autosaved bytes
          TTreeFormula* fVar1            Pointer to first variable formula
          TTreeFormula* fVar2            Pointer to second variable formula
          TTreeFormula* fVar3            Pointer to third variable formula
          TTreeFormula* fVar4            Pointer to fourth variable formula
          TTreeFormula* fSelect          Pointer to selection formula
          TTreeFormula* fMultiplicity    Pointer to formula giving ndata per entry
                  Int_t fChainOffset     Offset of 1st entry of this Tree in a TChain
                  Int_t fReadEntry       Number of the entry being processed
                  Int_t fTotalBuffers    Total number of bytes in branch buffers
                  Int_t fEstimate        Number of entries to estimate histogram limits
                  Int_t fDimension       Dimension of the current expression
                  Int_t fSelectedRows    Number of selected entries
                  Int_t fPacketSize      Number of entries in one packet for parallel root
                  Int_t fNbins[4]        Number of bins per dimension
                Float_t fVmin[4]         Minima of varexp columns
                Float_t fVmax[4]         Maxima of varexp columns
               Float_t* fV1              Local buffer for variable 1
               Float_t* fV2              Local buffer for variable 2
               Float_t* fV3              Local buffer for variable 3
              Double_t* fW               Local buffer for weights
            TDirectory* fDirectory       Pointer to directory holding this tree
              TObjArray fBranches        List of Branches
              TObjArray fLeaves          Direct pointers to individual branch leaves
                 TList* fActiveBranches  List of active branches
            TEventList* fEventList       Pointer to event selection list (if one)
             TSelector* fSelector        Pointer to current selector
      TPacketGenerator* fPacketGen       Packet generator
                  Int_t fNfill           Local for EntryLoop
                  Int_t fTimerInterval   Timer interval in milliseconds
                TArrayD fIndex           Sorted index of integer pairs

See also

TChain, TNtuple

Class Description

                                                                      
 TTree                                                                
                                                                      
  a TTree object has a header with a name and a title.
  It consists of a list of independent branches (TBranch). Each branch
  has its own definition and list of buffers. Branch buffers may be
  automatically written to disk or kept in memory until the Tree attribute
  fMaxVirtualSize is reached.
  Variables of one branch are written to the same buffer.
  A branch buffer is automatically compressed if the file compression
  attribute is set (default).

  Branches may be written to different files (see TBranch::SetFile).

  The ROOT user can decide to make one single branch and serialize one
  object into one single I/O buffer or to make several branches.
  Making one single branch and one single buffer can be the right choice
  when one wants to process only a subset of all entries in the tree.
  (you know for example the list of entry numbers you want to process).
  Making several branches is particularly interesting in the data analysis
  phase, when one wants to histogram some attributes of an object (entry)
  without reading all the attributes.

/*

*/


  ==> TTree *tree = new TTree(name, title, maxvirtualsize)
     Creates a Tree with name and title. Maxvirtualsize is by default 64Mbytes,
     maxvirtualsize = 64000000(default) means: Keeps as many buffers in memory until
     the sum of all buffers is greater than 64 Megabyte. When this happens,
     memory buffers are written to disk and deleted until the size of all
     buffers is again below the threshold.
     maxvirtualsize = 0 means: keep only one buffer in memory.

     Various kinds of branches can be added to a tree:
       A - simple structures or list of variables. (may be for C or Fortran structures)
       B - any object (inheriting from TObject). (we expect this option be the most frequent)
       C - a ClonesArray. (a specialized object for collections of same class objects)

  ==> Case A
      ======
     TBranch *branch = tree->Branch(branchname,address, leaflist, bufsize)
       * address is the address of the first item of a structure
       * leaflist is the concatenation of all the variable names and types
         separated by a colon character :
         The variable name and the variable type are separated by a slash (/).
         The variable type may be 0,1 or 2 characters. If no type is given,
         the type of the variable is assumed to be the same as the previous
         variable. If the first variable does not have a type, it is assumed
         of type F by default. The list of currently supported types is given below:
            - C : a character string terminated by the 0 character
            - B : an 8 bit signed integer (Char_t)
            - b : an 8 bit unsigned integer (UChar_t)
            - S : a 16 bit signed integer (Short_t)
            - s : a 16 bit unsigned integer (UShort_t)
            - I : a 32 bit signed integer (Int_t)
            - i : a 32 bit unsigned integer (UInt_t)
            - F : a 32 bit floating point (Float_t)
            - D : a 64 bit floating point (Double_t)

  ==> Case B
      ======
     TBranch *branch = tree->Branch(branchname,className,object, bufsize, splitlevel)
          object is the address of a pointer to an existing object (derived from TObject).
        if splitlevel=1 (default), this branch will automatically be split
          into subbranches, with one subbranch for each data member or object
          of the object itself. In case the object member is a TClonesArray,
          the mechanism described in case C is applied to this array.
        if splitlevel=0, the object is serialized in the branch buffer.

  ==> Case C
      ======
     TBranch *branch = tree->Branch(branchname,clonesarray, bufsize, splitlevel)
         clonesarray is the address of a pointer to a TClonesArray.
         The TClonesArray is a direct access list of objects of the same class.
         For example, if the TClonesArray is an array of TTrack objects,
         this function will create one subbranch for each data member of
         the object TTrack.


  ==> branch->SetAddress(Void *address)
      In case of dynamic structures changing with each entry for example, one must
      redefine the branch address before filling the branch again.
      This is done via the TBranch::SetAddress member function.

  ==> tree->Fill()
      loops on all defined branches and for each branch invokes the Fill function.

         See also the class TNtuple (a simple Tree with only one branch)

/*

*/

  =============================================================================
______________________________________________________________________________
*-*-*-*-*-*-*A simple example with histograms and a tree*-*-*-*-*-*-*-*-*-*
*-*          ===========================================

  This program creates :
    - a one dimensional histogram
    - a two dimensional histogram
    - a profile histogram
    - a tree

  These objects are filled with some random numbers and saved on a file.

-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*

 #include "TROOT.h"
 #include "TFile.h"
 #include "TH1.h"
 #include "TH2.h"
 #include "TProfile.h"
 #include "TRandom.h"
 #include "TTree.h"


 TROOT simple("simple","Histograms and trees");

 //______________________________________________________________________________
 main(int argc, char **argv)
 {
 // Create a new ROOT binary machine independent file.
 // Note that this file may contain any kind of ROOT objects, histograms,trees
 // pictures, graphics objects, detector geometries, tracks, events, etc..
 // This file is now becoming the current directory.
   TFile hfile("htree.root","RECREATE","Demo ROOT file with histograms & trees");

 // Create some histograms and a profile histogram
   TH1F *hpx   = new TH1F("hpx","This is the px distribution",100,-4,4);
   TH2F *hpxpy = new TH2F("hpxpy","py ps px",40,-4,4,40,-4,4);
   TProfile *hprof = new TProfile("hprof","Profile of pz versus px",100,-4,4,0,20);

 // Define some simple structures
   typedef struct {Float_t x,y,z;} POINT;
   typedef struct {
      Int_t ntrack,nseg,nvertex;
      UInt_t flag;
      Float_t temperature;
   } EVENTN;
   static POINT point;
   static EVENTN eventn;

 // Create a ROOT Tree
   TTree *tree = new TTree("T","An example of ROOT tree with a few branches");
   tree->Branch("point",&point,"x:y:z");
   tree->Branch("eventn",&eventn,"ntrack/I:nseg:nvertex:flag/i:temperature/F");
   tree->Branch("hpx","TH1F",&hpx,128000,0);

   Float_t px,py,pz;
   static Float_t p[3];

 //--------------------Here we start a loop on 1000 events
   for ( Int_t i=0; i<1000; i++) {
      gRandom->Rannor(px,py);
      pz = px*px + py*py;
      Float_t random = gRandom->::Rndm(1);

 //         Fill histograms
      hpx->Fill(px);
      hpxpy->Fill(px,py,1);
      hprof->Fill(px,pz,1);

 //         Fill structures
      p[0] = px;
      p[1] = py;
      p[2] = pz;
      point.x = 10*(random-1);;
      point.y = 5*random;
      point.z = 20*random;
      eventn.ntrack  = Int_t(100*random);
      eventn.nseg    = Int_t(2*eventn.ntrack);
      eventn.nvertex = 1;
      eventn.flag    = Int_t(random+0.5);
      eventn.temperature = 20+random;

 //        Fill the tree. For each event, save the 2 structures and 3 objects
 //      In this simple example, the objects hpx, hprof and hpxpy are slightly
 //      different from event to event. We expect a big compression factor!
      tree->Fill();
   }
  //--------------End of the loop

   tree->Print();

 // Save all objects in this file
   hfile.Write();

 // Close the file. Note that this is automatically done when you leave
 // the application.
   hfile.Close();

   return 0;
 }
                                                                      

*-*-*-*-*-*-*-*-*-*-*Default Tree constructor*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                  ========================

*-*-*-*-*-*-*-*-*-*Normal Tree constructor*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                ======================

   The Tree is created in the current directory
   Use the various functions Branch below to add branches to this Tree.

*-*-*-*-*-*-*-*-*-*-*Tree destructor*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                  =================

*-*-*-*-*-*-*-*-*-*-*AutoSave tree header every fAutoSave bytes*-*-*-*-*-*
*-*                  ==========================================

   When large Trees are produced, it is safe to activate the AutoSave
   procedure. Some branches may have buffers holding many entries.
   AutoSave is automatically called by TTree::Fill when the number of bytes
   generated since the previous AutoSave is greater than fAutoSave bytes.
   This function may also be invoked by the user, for example every
   N entries.
   Each AutoSave generates a new key on the file.

   In case your program crashes before closing the file holding this tree,
   the file will be automatically recovered when you will connect the file
   in UPDATE mode.
   The Tree will be recovered at the status corresponding to the last AutoSave.

*-*-*-*-*-*-*-*-*-*-*Create a new TTree Branch*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                  =========================

     This Branch constructor is provided to support non-objects in
     a Tree. The variables described in leaflist may be simple variables
     or structures.
    See the two following constructors for writing objects in a Tree.

    By default the branch buffers are stored in the same file as the Tree.
    use TBranch::SetFile to specify a different file

*-*-*-*-*-*-*-*-*-*-*Create a new TTree BranchObject*-*-*-*-*-*-*-*-*-*-*-*
*-*                  ===============================

    Build a TBranchObject for an object of class classname.
    addobj is the address of a pointer to an object of class classname.
    IMPORTANT: classname must derive from TObject.

    This option requires access to the library where the corresponding class
    is defined. Accessing one single data member in the object implies
    reading the full object.
    See the next Branch constructor for a more efficient storage
    in case the entry consists of arrays of identical objects.

    By default the branch buffers are stored in the same file as the Tree.
    use TBranch::SetFile to specify a different file

*-*-*-*-*-*-*-*-*-*-*Create a new TTree BranchClones*-*-*-*-*-*-*-*-*-*-*-*
*-*                  ===============================

    name:    global name of this BranchClones
    bufsize: buffersize in bytes of each individual data member buffer
    clonesaddress is the address of a pointer to a TClonesArray.

    This Tree option is provided in case each entry consists of one
    or more arrays of same class objects (tracks, hits,etc).
    This function creates as many branches as there are public data members
    in the objects pointed by the TClonesArray. Note that these data members
    can be only basic data types, not pointers or objects.

    BranchClones have the following advantages compared to the two other
    solutions (Branch and BranchObject).
      - When reading the Tree data, it is possible to read selectively
        a subset of one object (may be just one single data member).
      - This solution minimizes the number of objects created/destructed.
      - Data members of the same type are consecutive in the basket buffers,
        therefore optimizing the compression algorithm.
      - Array processing notation becomes possible in the query language.

    By default the branch buffers are stored in the same file as the Tree.
    use TBranch::SetFile to specify a different file

 Build an index table using the leaves with name: major & minor name
 The index is built in the following way:
    A pass on all entries is made using TTree::Draw
    var1 = majorname
    var2 = minorname
    sel  = majorname +minorname*1e-9
    The standard result from TTree::Draw is stored in fV1, fV2 and fW
    Thew array fW is sorted into fIndex
  Once the index is computed, one can retrieve one entry via
    TTree:GetEntryWithIndex(majornumber, minornumber)
 Example:
  tree.BuildIndex("Run","Event"); //creates an index using leaves Run and Event
  tree.GetEntryWithIndex(1234,56789); //reads entry corresponding to
                                        Run=1234 and Event=56789

 Note that once the index is built, it can be saved with the TTree object
 with tree.Write(); //if the file has been open in "update" mode.

 The most convenient place to create the index is at the end of
 the filling process just before saving the Tree header.
 If a previous index was computed, it is redefined by this new call.

 Note that this function can also be applied to a TChain.

*-*-*-*-*-*-*Delete internal buffers*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*          =======================

 Create a clone of this tree and copy nentries
 By default copy all entries

 IMPORTANT: Before invoking this function, the branch addresses
            of this TTree must have been set.
 For examples of CloneTree, see tutorials
  -copytree:
    Example of Root macro to copy a subset of a Tree to a new Tree
    The input file has been generated by the program in $ROOTSYS/test/Event
    with   Event 1000 1 1 1
  -copytree2:
    Example of Root macro to copy a subset of a Tree to a new Tree
    One branch of the new Tree is written to a separate file
    The input file has been generated by the program in $ROOTSYS/test/Event
    with   Event 1000 1 1 1

*-*-*-*-*-*-*Compile input variables and selection expression*-*-*-*-*-*
*-*          ================================================

  varexp is an expression of the general form e1:e2:e3
    where e1,etc is a formula referencing a combination of the columns
  Example:
     varexp = x     simplest case: draw a 1-Dim distribution of column named x
            = sqrt(x)            : draw distribution of sqrt(x)
            = x*y/z
            = y:sqrt(x) 2-Dim dsitribution of y versus sqrt(x)

  selection is an expression with a combination of the columns
  Example:
      selection = "x<y && sqrt(z)>3.2"
       in a selection all the C++ operators are authorized

 Copy nentries from tree to this tree
 By default copy all entries
 Return number of bytes copied to this tree.

 Create or reset the packet generator.

*-*-*-*-*-*-*-*-*-*-*Draw expression varexp for specified entries-*-*-*-*-*
*-*                  ===========================================

      This function accepts TCut objects as arguments.
      Useful to use the string operator +
         example:
            ntuple.Draw("x",cut1+cut2+cut3);

*-*-*-*-*-*-*-*-*-*-*Draw expression varexp for specified entries-*-*-*-*-*
*-*                  ===========================================

  varexp is an expression of the general form e1:e2:e3
    where e1,etc is a formula referencing a combination of the columns
  Example:
     varexp = x     simplest case: draw a 1-Dim distribution of column named x
            = sqrt(x)            : draw distribution of sqrt(x)
            = x*y/z
            = y:sqrt(x) 2-Dim dsitribution of y versus sqrt(x)
  Note that the variables e1, e2 or e3 may contain a selection.
  example, if e1= x*(y<0), the value histogrammed will be x if y<0
  and will be 0 otherwise.

  selection is an expression with a combination of the columns.
  In a selection all the C++ operators are authorized.
  The value corresponding to the selection expression is used as a weight
  to fill the histogram.
  If the expression includes only boolean operations, the result
  is 0 or 1. If the result is 0, the histogram is not filled.
  In general, the expression may be of the form:
      value*(boolean expression)
  if boolean expression is true, the histogram is filled with
  a weight = value.
  Examples:
      selection1 = "x<y && sqrt(z)>3.2"
      selection2 = "(x+y)*(sqrt(z)>3.2"
  selection1 returns a weigth = 0 or 1
  selection2 returns a weight = x+y if sqrt(z)>3.2
             returns a weight = 0 otherwise.

  option is the drawing option
      see TH1::Draw for the list of all drawing options.
      If option contains the string "goff", no graphics is generated.

  nentries is the number of entries to process (default is all)
  first is the first entry to process (default is 0)

     Saving the result of Draw to an histogram
     =========================================
  By default the temporary histogram created is called htemp.
  If varexp0 contains >>hnew (following the variable(s) name(s),
  the new histogram created is called hnew and it is kept in the current
  directory.
  Example:
    tree.Draw("sqrt(x)>>hsqrt","y>0")
    will draw sqrt(x) and save the histogram as "hsqrt" in the current
    directory.

  By default, the specified histogram is reset.
  To continue to append data to an existing histogram, use "+" in front
  of the histogram name;
    tree.Draw("sqrt(x)>>+hsqrt","y>0")
      will not reset hsqrt, but will continue filling.

     Making a Profile histogram
     ==========================
  In case of a 2-Dim expression, one can generate a TProfile histogram
  instead of a TH2F histogram by specyfying option=prof or option=profs.
  The option=prof is automatically selected in case of y:x>>pf
  where pf is an existing TProfile histogram.

     Saving the result of Draw to a TEventList
     =========================================
  TTree::Draw can be used to fill a TEventList object (list of entry numbers)
  instead of histogramming one variable.
  If varexp0 has the form >>elist , a TEventList object named "elist"
  is created in the current directory. elist will contain the list
  of entry numbers satisfying the current selection.
  Example:
    tree.Draw(">>yplus","y>0")
    will create a TEventList object named "yplus" in the current directory.
    In an interactive session, one can type (after TTree::Draw)
       yplus.Print("all")
    to print the list of entry numbers in the list.

  By default, the specified entry list is reset.
  To continue to append data to an existing list, use "+" in front
  of the list name;
    tree.Draw(">>+yplus","y>0")
      will not reset yplus, but will enter the selected entries at the end
      of the existing list.

      Using a TEventList as Input
      ===========================
  Once a TEventList object has been generated, it can be used as input
  for TTree::Draw. Use TTree::SetEventList to set the current event list
  Example:
     TEventList *elist = (TEventList*)gDirectory->Get("yplus");
     tree->SetEventList(elist);
     tree->Draw("py");

  Note: Use tree->SetEventList(0) if you do not want use the list as input.

      How to obtain more info from TTree::Draw
      ========================================

  Once TTree::Draw has been called, it is possible to access useful
  information still stored in the TTree object via the following functions:
    -GetSelectedRows()    // return the number of entries accepted by the
                          //selection expression. In case where no selection
                          //was specified, returns the number of entries processed.
    -GetV1()              //returns a pointer to the float array of V1
    -GetV2()              //returns a pointer to the float array of V2
    -GetV3()              //returns a pointer to the float array of V3
    -GetW()               //returns a pointer to the double array of Weights
                          //where weight equal the result of the selection expression.
   where V1,V2,V3 correspond to the expressions in
   TTree::Draw("V1:V2:V3",selection);

   Example:
    Root > ntuple->Draw("py:px","pz>4");
    Root > TGraph *gr = new TGraph(ntuple->GetSelectedRows(),
                                   ntuple->GetV2(), ntuple->GetV1());
    Root > gr->Draw("ap"); //draw graph in current pad
    creates a TGraph object with a number of points corresponding to the
    number of entries selected by the expression "pz>4", the x points of the graph
    being the px values of the Tree and the y points the py values.

   Important note: By default TTree::Draw creates the arrays obtained
    with GetV1, GetV2, GetV3, GetW with a length corresponding to the
    parameter fEstimate. By default fEstimate=10000 and can be modified
    via TTree::SetEstimate. A possible recipee is to do
       tree->SetEstimate(tree->GetEntries());
    You must call SetEstimate if the expected number of selected rows
    is greater than 10000.

    You can use the option "goff" to turn off the graphics output
    of TTree::Draw in the above example.

           Automatic interface to TTree::Draw via the TTreeViewer
           ======================================================

    A complete graphical interface to this function is implemented
    in the class TTreeViewer.
    To start the TTreeViewer, three possibilities:
       - select TTree context menu item "StartViewer"
       - type the command  "TTreeViewer TV(treeName)"
       - execute statement "tree->StartViewer();"

*-*-*-*-*Drop branch buffers to accomodate nbytes below MaxVirtualsize*-*-*-*

*-*-*-*-*Estimate histogram limits for conditions of input parameters*-*-*-*
*-*      ============================================================

  The estimation of the limits is based on estimate entries
  The first estimate/2 and the last esstimate/2 entries are used.
  This algorithm is in general good enough to make a reasonable estimation
  with a small number of entries.

  nentries is the number of entries to process (default is all)
  first is the first entry to process (default is 0)

*-*-*-*-*-*-*-*-*-*-*-*-*Loop on all entries*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      ==================

  nentries is the number of entries to process (default is all)
  first is the first entry to process (default is 0)

  action =  1  Fill 1-D histogram obj
         =  2  Fill 2-D histogram obj
         =  3  Fill 3-D histogram obj
         =  4  Fill Profile histogram obj
         =  5  Fill a TEventlist
         = 11  Estimate Limits
         = 12  Fill 2-D PolyMarker obj
         = 13  Fill 3-D PolyMarker obj
  action < 0   Evaluate Limits for case abs(action)

*-*-*-*-*Fill all branches of a Tree*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*      ===========================

   This function loops on all the branches of this tree.
   For each branch, it copies to the branch buffer (basket) the current
   values of the leaves data types.
   If a leaf is a simple data type, a simple conversion to a machine
   independent format has to be done.

*-*-*-*-*-*-*-*-*Find reasonable bin values*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*              ==========================

*-*-*-*-*-*-*-*-*Fit  a projected item(s) from a Tree*-*-*-*-*-*-*-*-*-*
*-*              ======================================

  formula is a TF1 expression.

  See TTree::Draw for explanations of the other parameters.

  By default the temporary histogram created is called htemp.
  If varexp contains >>hnew , the new histogram created is called hnew
  and it is kept in the current directory.
  Example:
    tree.Fit(pol4,sqrt(x)>>hsqrt,y>0)
    will fit sqrt(x) and save the histogram as "hsqrt" in the current
    directory.

*-*-*-*-*-*Return pointer to the branch with name*-*-*-*-*-*-*-*
*-*        ======================================

*-*-*-*-*-*Return pointer to the current file*-*-*-*-*-*-*-*
*-*        ==================================

*-*-*-*-*-*Read all branches of entry and return total number of bytes*-*-*
*-*        ===========================================================
     getall = 0 : get only active branches
     getall = 1 : get all branches

*-*-*-*-*-*Return entry number corresponding to entry*-*-*
*-*        ==========================================
     if no selection list returns entry
     else returns the entry number corresponding to the list index=entry

 Return entry number corresponding to major and minor number

 Return entry  corresponding to major and minor number
 For example:
     Int_t run   = 1234;
     Int_t event = 345;
     Int_t serial= tree.GetEntryNumberWithIndex(run,event);
    now the variable serial is in the range [0,nentries] and one can do
    tree.GetEntry(serial);

*-*-*-*-*-*Return pointer to the 1st Leaf named name in any Branch-*-*-*-*-*
*-*        =======================================================

*-*-*-*-*-*-*-*-*Return maximum of column with name columname*-*-*-*-*-*-*
*-*              ============================================

*-*-*-*-*-*-*-*-*Return minimum of column with name columname*-*-*-*-*-*-*
*-*              ============================================

*-*-*-*-*-*-*-*-*Return name corresponding to colindex in varexp*-*-*-*-*-*
*-*              ===============================================

   varexp is a string of names separated by :
   index is an array with pointers to the start of name[i] in varexp

 Return in nentries and firstentry the optimal range of entries (packet)
 to be processed by slave sl. See TPacketGenerator for the algorithm
 used to get the packet size.

*-*-*-*-*-*Return current selector or create default selector
*-*        ==================================================

*-*-*-*-*-*-*-*-*Set current Tree entry
*-*              ======================

*-*-*-*-*-*-*-*-*Loop on nentries of this tree starting at firstentry
*-*              ===================================================

*-*-*-*-*-*-*-*-*Fill Hoption structure with the codes in option*-*-*-*-*-*
*-*              ===============================================

====>
*-*-*-*-*-*-*Generate skeleton analysis class for this Tree*-*-*-*-*-*-*
*-*          ==============================================

   The following files are produced: classname.h and classname.C
   if classname is NULL, classname will be nameoftree.

   The generated code in classname.h includes the following:
      - Identification of the original Tree and Input file name
      - Definition of analysis class (data and functions)
      - the following class functions:
         -constructor (connecting by default the Tree file)
         -GetEntry(Int_t entry)
         -Init(TTree *tree) to initialize a new TTree
         -Show(Int_t entry) to read and Dump entry

   The generated code in classname.C includes only the main
   analysis function Loop.

   To use this function:
      - connect your Tree file (eg: TFile f("myfile.root");)
      - T->MakeClass("MyClass");
    where T is the name of the Tree in file myfile.root
    and MyClass.h, MyClass.C the name of the files created by this function.
   In a Root session, you can do:
      Root > .L MyClass.C
      Root > MyClass t
      Root > t.GetEntry(12); // Fill t data members with entry number 12
      Root > t.Show();       // Show values of entry 12
      Root > t.Show(16);     // Read and show values of entry 16
      Root > t.Loop();       // Loop on all entries

====>

====>
*-*-*-*-*-*-*-*-*Generate skeleton function for this Tree*-*-*-*-*-*-*
*-*              ========================================

   The function code is written on filename
   if filename is NULL, filename will be nameoftree.C

   The generated code includes the following:
      - Identification of the original Tree and Input file name
      - Connection of the Tree file
      - Declaration of Tree variables
      - Setting of branches addresses
      - a skeleton for the entry loop

   To use this function:
      - connect your Tree file (eg: TFile f("myfile.root");)
      - T->MakeCode("anal.C");
    where T is the name of the Tree in file myfile.root
    and anal.C the name of the file created by this function.

   NOTE: Since the implementation of this function, a new and better
         function TTree::MakeClass has been developped.

          Author: Rene Brun
====>

*-*-*-*-*-*-*-*-*Fill Foption structure with the codes in option*-*-*-*-*-*
*-*              ===============================================

*-*-*-*-*-*-*-*-*Build Index array for names in varexp*-*-*-*-*-*-*-*-*-*-*
*-*              =====================================

*-*-*-*-*-*Check if adding nbytes to memory we are still below MaxVirtualsize
*-*        ==================================================================

 Print a summary of the Tree contents. In case options are "p" or "pa"
 print information about the TPacketGenerator ("pa" is equivalent to
 TPacketGenerator::Print("all")).

*-*-*-*-*-*-*-*-*Make a projection of a Tree using selections*-*-*-*-*-*-*
*-*              =============================================

   Depending on the value of varexp (described in Draw) a 1-D,2-D,etc
   projection of the Tree will be filled in histogram hname.
   Note that the dimension of hname must match with the dimension of varexp.

*-*-*-*-*-*-*-*Reset buffers and entries count in all branches/leaves*-*-*
*-*            ======================================================

*-*-*-*-*-*-*-*-*Loop on Tree & print entries following selection*-*-*-*-*-*
*-*              ===============================================

*-*-*-*-*-*-*-*-*Set branch address*-*-*-*-*-*-*-*
*-*              ==================

      If object is a TTree, this function is only an interface to TBranch::SetAddress
      Function overloaded by TChain.

*-*-*-*-*-*-*-*-*Set branch status Process or DoNotProcess*-*-*-*-*-*-*-*
*-*              =========================================

      bname is the name of a branch. if bname="*", apply to all branches.
      status = 1  branch will be processed
             = 0  branch will not be processed

 Remove reference to this tree from current directory and add
 reference to new directory dir. dir can be 0 in which case the tree
 does not belong to any directory.

*-*-*-*-*-*-*-*-*Set number of entries to estimate variable limits*-*-*-*
*-*              ================================================

*-*-*-*-*-*-*-*-*-*-*Change the name of this Tree*-*-*-*-*-*-*-*-*-*-*
*-*                  ============================

*-*-*-*-*-*-*-*-*Set number of entries per packet for parallel root*-*-*-*-*
*-*              =================================================

*-*-*-*-*-*-*-*-*Set current selector to user selector*-*-*-*-*-*-*-*
*-*              =====================================

*-*-*-*-*-*-*-*-*Set current selector to macroname*-*-*-*-*-*-*-*
*-*              =================================

*-*-*-*-*-*Print values of all active leaves for entry*-*-*-*-*-*-*-*
*-*        ===========================================
 if entry==-1, print current entry (default)

*-*-*-*-*-*-*-*-*Start the TTreeViewer on this TTree*-*-*-*-*-*-*-*-*-*
*-*              ===================================

  ww is the width of the canvas in pixels
  wh is the height of the canvas in pixels

*-*-*-*-*-*-*-*-*Stream a class object*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*              =========================================

*-*-*-*-*-*Execute action for object obj nfill times*-*-*-*-*-*-*-*-*-*
*-*        =========================================

*-*-*-*-*-*Estimate limits for 1-D, 2-D or 3-D objects*-*-*-*-*-*-*-*-*-*
*-*        ===========================================

*-*-*-*-*-*-*-*-*Build the list of active branches*-*-*-*-*-*-*-*
*-*              =================================

   Scan all branches and enter branches with active status in fActiveBranches.

Inline Functions

                     void AddTotBytes(Int_t tot)
                     void AddZipBytes(Int_t zip)
                     void Draw(Text_t* varexp, Text_t* selection, Option_t* option, Int_t nentries = 1000000000, Int_t firstentry = 0)
                    Int_t GetChainOffset()
              TDirectory* GetDirectory()
                   Stat_t GetEntries()
                    Int_t GetEstimate()
                    Int_t GetEvent(Int_t entry = 0, Int_t getall = 0)
              TEventList* GetEventList()
                Double_t* GetIndex()
                   TList* GetListOfActiveBranches()
               TObjArray* GetListOfBranches()
               TObjArray* GetListOfLeaves()
                    Int_t GetMaxEntryLoop()
                    Int_t GetMaxVirtualSize()
            TTreeFormula* GetMultiplicity()
                    Int_t GetNbranches()
        TPacketGenerator* GetPacketGenerator()
                    Int_t GetPacketSize()
                    Int_t GetReadEntry()
                    Int_t GetReadEvent()
                    Int_t GetScanField()
            TTreeFormula* GetSelect()
                    Int_t GetSelectedRows()
            TTreeFormula* GetVar1()
            TTreeFormula* GetVar2()
            TTreeFormula* GetVar3()
            TTreeFormula* GetVar4()
                 Float_t* GetV1()
                 Float_t* GetV2()
                 Float_t* GetV3()
                Double_t* GetW()
                   Stat_t GetTotBytes()
                   Stat_t GetZipBytes()
                     void IncrementTotalBuffers(Int_t nbytes)
                   Bool_t IsFolder()
                     void SetAutoSave(Int_t autosave = 10000000)
                     void SetChainOffset(Int_t offset = 0)
                     void SetEventList(TEventList* list)
                     void SetMaxEntryLoop(Int_t maxev = 1000000000)
                     void SetMaxVirtualSize(Int_t size = 0)
                     void SetScanField(Int_t n = 50)
                     void SetTimerInterval(Int_t msec = 333)
                     void SetUpdate(Int_t freq = 0)
                  TClass* Class()
                  TClass* IsA()
                     void ShowMembers(TMemberInspector& insp, char* parent)
                    TTree TTree(TTree&)