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

 Default constructor and I/O constructor.

 Note: We do *not* insert ourself into the current directory.

 Normal tree constructor.

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

 If the first character of title is a "/", the function assumes a folder name.
 In this case, it creates automatically branches following the folder hierarchy.
 splitlevel may be used in this case to control the split level.

 Destructor.

 Returns the transient buffer currently used by this TTree for reading/writing baskets.

 Add branch with name bname to the Tree cache.
 If bname="*" all branches are added to the cache.
 if subbranches is true all the branches of the subbranches are
 also put to the cache.

 Add branch b to the Tree cache.
 if subbranches is true all the branches of the subbranches are
 also put to the cache.

 Remove the branch with name 'bname' from the Tree cache.
 If bname="*" all branches are removed from the cache.
 if subbranches is true all the branches of the subbranches are
 also removed from the cache.

 Remove the branch b from the Tree cache.
 if subbranches is true all the branches of the subbranches are
 also removed from the cache.

 Add a cloned tree to our list of trees to be notified whenever we change
 our branch addresses or when we are deleted.

 Add a TFriendElement to the list of friends.

 This function:
   -opens a file if filename is specified
   -reads a Tree with name treename from the file (current directory)
   -adds the Tree to the list of friends
 see other AddFriend functions

 A TFriendElement TF describes a TTree object TF in a file.
 When a TFriendElement TF is added to the the list of friends of an
 existing TTree T, any variable from TF can be referenced in a query
 to T.

   A tree keeps a list of friends. In the context of a tree (or a chain),
 friendship means unrestricted access to the friends data. In this way
 it is much like adding another branch to the tree without taking the risk
 of damaging it. To add a friend to the list, you can use the TTree::AddFriend
 method.  The tree in the diagram below has two friends (friend_tree1 and
 friend_tree2) and now has access to the variables a,b,c,i,j,k,l and m.

 The AddFriend method has two parameters, the first is the tree name and the
 second is the name of the ROOT file where the friend tree is saved.
 AddFriend automatically opens the friend file. If no file name is given,
 the tree called ft1 is assumed to be in the same file as the original tree.

 tree.AddFriend("ft1","friendfile1.root");
 If the friend tree has the same name as the original tree, you can give it
 an alias in the context of the friendship:

 tree.AddFriend("tree1 = tree","friendfile1.root");
 Once the tree has friends, we can use TTree::Draw as if the friend's
 variables were in the original tree. To specify which tree to use in
 the Draw method, use the syntax:

 <treeName>.<branchname>.<varname>
 If the variablename is enough to uniquely identify the variable, you can
 leave out the tree and/or branch name.
 For example, these commands generate a 3-d scatter plot of variable "var"
 in the TTree tree versus variable v1 in TTree ft1 versus variable v2 in
 TTree ft2.

 tree.AddFriend("ft1","friendfile1.root");
 tree.AddFriend("ft2","friendfile2.root");
 tree.Draw("var:ft1.v1:ft2.v2");

 The picture illustrates the access of the tree and its friends with a
 Draw command.
 When AddFriend is called, the ROOT file is automatically opened and the
 friend tree (ft1) is read into memory. The new friend (ft1) is added to
 the list of friends of tree.
 The number of entries in the friend must be equal or greater to the number
 of entries of the original tree. If the friend tree has fewer entries a
 warning is given and the missing entries are not included in the histogram.
 To retrieve the list of friends from a tree use TTree::GetListOfFriends.
 When the tree is written to file (TTree::Write), the friends list is saved
 with it. And when the tree is retrieved, the trees on the friends list are
 also retrieved and the friendship restored.
 When a tree is deleted, the elements of the friend list are also deleted.
 It is possible to declare a friend tree that has the same internal
 structure (same branches and leaves) as the original tree, and compare the
 same values by specifying the tree.

  tree.Draw("var:ft1.var:ft2.var")

 Add a TFriendElement to the list of friends.

 The TFile is managed by the user (e.g. the user must delete the file).
 For complete description see AddFriend(const char *, const char *).
 This function:
   -reads a Tree with name treename from the file
   -adds the Tree to the list of friends

 Add a TFriendElement to the list of friends.

 The TTree is managed by the user (e.g., the user must delete the file).
 For a complete description see AddFriend(const char *, const char *).

 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.
   If fAutoSave is negative, AutoSave is automatically called by
   TTree::Fill when the number of bytes generated since the previous
   AutoSave is greater than -fAutoSave bytes.
   If fAutoSave is positive, AutoSave is automatically called by
   TTree::Fill every N entries.
   This function may also be invoked by the user.
   Each AutoSave generates a new key on the file.
   Once the key with the tree header has been written, the previous cycle
   (if any) is deleted.

   Note that calling TTree::AutoSave too frequently (or similarly calling
   TTree::SetAutoSave with a small value) is an expensive operation.
   You should make tests for your own application to find a compromise
   between speed and the quantity of information you may loose in case of
   a job crash.

   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.

   if option contains "SaveSelf", gDirectory->SaveSelf() is called.
   This allows another process to analyze the Tree while the Tree is being filled.

   if option contains "FlushBaskets", TTree::FlushBaskets is called and all
   the current basket are closed-out and written to disk individually.

   By default the previous header is deleted after having written the new header.
   if option contains "Overwrite", the previous Tree header is deleted
   before written the new header. This option is slightly faster, but
   the default option is safer in case of a problem (disk quota exceeded)
   when writing the new header.

   The function returns the number of bytes written to the file.
   if the number of bytes is null, an error has occurred while writing
   the header to the file.

   How to write a Tree in one process and view it from another process

   The following two scripts illustrate how to do this.
   The script treew.C is executed by process1, treer.C by process2

   ----- script treew.C
   void treew() {
     TFile f("test.root","recreate");
     TNtuple *ntuple = new TNtuple("ntuple","Demo","px:py:pz:random:i");
     Float_t px, py, pz;
     for ( Int_t i=0; i<10000000; i++) {
        gRandom->Rannor(px,py);
        pz = px*px + py*py;
        Float_t random = gRandom->Rndm(1);
        ntuple->Fill(px,py,pz,random,i);
        if (i%1000 == 1) ntuple->AutoSave("SaveSelf");
     }
   }

   ----- script treer.C
   void treer() {
      TFile f("test.root");
      TTree *ntuple = (TTree*)f.Get("ntuple");
      TCanvas c1;
      Int_t first = 0;
      while(1) {
         if (first == 0) ntuple->Draw("px>>hpx", "","",10000000,first);
         else            ntuple->Draw("px>>+hpx","","",10000000,first);
         first = (Int_t)ntuple->GetEntries();
         c1.Update();
         gSystem->Sleep(1000); //sleep 1 second
         ntuple->Refresh();
      }
   }

 Same as TTree::Branch() with added check that addobj matches className.

 See TTree::Branch() for other details.

 Same as TTree::Branch but automatic detection of the class name.
 See TTree::Branch for other details.

 Same as TTree::Branch but automatic detection of the class name.
 See TTree::Branch for other details.

 Same as TTree::Branch but automatic detection of the class name.
 See TTree::Branch for other details.

 Deprecated function. Use next function instead.

 Create one branch for each element in the collection.

   Each entry in the collection becomes a top level branch if the
   corresponding class is not a collection. If it is a collection, the entry
   in the collection becomes in turn top level branches, etc.
   The splitlevel is decreased by 1 every time a new collection is found.
   For example if list is a TObjArray*
     - if splitlevel = 1, one top level branch is created for each element
        of the TObjArray.
     - if splitlevel = 2, one top level branch is created for each array element.
       if, in turn, one of the array elements is a TCollection, one top level
       branch will be created for each element of this collection.

   In case a collection element is a TClonesArray, the special Tree constructor
   for TClonesArray is called.
   The collection itself cannot be a TClonesArray.

   The function returns the total number of branches created.

   If name is given, all branch names will be prefixed with name_.

 IMPORTANT NOTE1: This function should not be called with splitlevel < 1.

 IMPORTANT NOTE2: The branches created by this function will have names
 corresponding to the collection or object names. It is important
 to give names to collections to avoid misleading branch names or
 identical branch names. By default collections have a name equal to
 the corresponding class name, e.g. the default name for a TList is "TList".

 And in general in any cases two or more master branches contain subbranches
 with identical names, one must add a "." (dot) character at the end
 of the master branch name. This will force the name of the subbranch
 to be master.subbranch instead of simply subbranch.
 This situation happens when the top level object (say event)
 has two or more members referencing the same class.
 For example, if a Tree has two branches B1 and B2 corresponding
 to objects of the same class MyClass, one can do:
       tree.Branch("B1.","MyClass",&b1,8000,1);
       tree.Branch("B2.","MyClass",&b2,8000,1);
 if MyClass has 3 members a,b,c, the two instructions above will generate
 subbranches called B1.a, B1.b ,B1.c, B2.a, B2.b, B2.c

 Example--------------------------------------------------------------:

   {
         TTree T("T","test list");
         TList *list = new TList();

         TObjArray *a1 = new TObjArray();
         a1->SetName("a1");
         list->Add(a1);
         TH1F *ha1a = new TH1F("ha1a","ha1",100,0,1);
         TH1F *ha1b = new TH1F("ha1b","ha1",100,0,1);
         a1->Add(ha1a);
         a1->Add(ha1b);
         TObjArray *b1 = new TObjArray();
         b1->SetName("b1");
         list->Add(b1);
         TH1F *hb1a = new TH1F("hb1a","hb1",100,0,1);
         TH1F *hb1b = new TH1F("hb1b","hb1",100,0,1);
         b1->Add(hb1a);
         b1->Add(hb1b);

         TObjArray *a2 = new TObjArray();
         a2->SetName("a2");
         list->Add(a2);
         TH1S *ha2a = new TH1S("ha2a","ha2",100,0,1);
         TH1S *ha2b = new TH1S("ha2b","ha2",100,0,1);
         a2->Add(ha2a);
         a2->Add(ha2b);

         T.Branch(list,16000,2);
         T.Print();
   }

 Create one branch for each element in the folder.
 Returns the total number of branches created.

 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

       * 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)
            - L : a 64 bit signed integer (Long64_t)
            - l : a 64 bit unsigned integer (ULong64_t)
            - O : [the letter 'o', not a zero] a boolean (Bool_t)

         Arrays of values are supported with the following syntax:
         If leaf name has the form var[nelem], where nelem is alphanumeric, then
            if nelem is a leaf name, it is used as the variable size of the array,
            otherwise return 0.
         If leaf name has the form var[nelem], where nelem is a non-negative integer, then
            it is used as the fixed size of the array.
         If leaf name has the form of a multi-dimensional array (e.g. var[nelem][nelem2])
            where nelem and nelem2 are non-negative integer) then
            it is used as a 2 dimensional array of fixed size.
         Any of other form is not supported.

    Note that the TTree will assume that all the item are contiguous in memory.
    On some platform, this is not always true of the member of a struct or a class,
    due to padding and alignment.  Sorting your data member in order of decreasing
    sizeof usually leads to their being contiguous in memory.

       * bufsize is the buffer size in bytes for this branch
         The default value is 32000 bytes and should be ok for most cases.
         You can specify a larger value (e.g. 256000) if your Tree is not split
         and each entry is large (Megabytes)
         A small value for bufsize is optimum if you intend to access
         the entries in the Tree randomly and your Tree is in split mode.

 Create a new branch with the object of class classname at address addobj.

 WARNING:
 Starting with Root version 3.01, the Branch function uses the new style
 branches (TBranchElement). To get the old behaviour, you can:
   - call BranchOld or
   - call TTree::SetBranchStyle(0)

 Note that with the new style, classname does not need to derive from TObject.
 It must derived from TObject if the branch style has been set to 0 (old)

 Note: See the comments in TBranchElement::SetAddress() for a more
       detailed discussion of the meaning of the addobj parameter in
       the case of new-style branches.

 Use splitlevel < 0 instead of splitlevel=0 when the class
 has a custom Streamer

 Note: if the split level is set to the default (99),  TTree::Branch will
 not issue a warning if the class can not be split.

 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.
    The class dictionary must be available (ClassDef in class header).

    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

      IMPORTANT NOTE about branch names
    In case two or more master branches contain subbranches with
    identical names, one must add a "." (dot) character at the end
    of the master branch name. This will force the name of the subbranch
    to be master.subbranch instead of simply subbranch.
    This situation happens when the top level object (say event)
    has two or more members referencing the same class.
    For example, if a Tree has two branches B1 and B2 corresponding
    to objects of the same class MyClass, one can do:
       tree.Branch("B1.","MyClass",&b1,8000,1);
       tree.Branch("B2.","MyClass",&b2,8000,1);
    if MyClass has 3 members a,b,c, the two instructions above will generate
    subbranches called B1.a, B1.b ,B1.c, B2.a, B2.b, B2.c

    bufsize is the buffer size in bytes for this branch
    The default value is 32000 bytes and should be ok for most cases.
    You can specify a larger value (e.g. 256000) if your Tree is not split
    and each entry is large (Megabytes)
    A small value for bufsize is optimum if you intend to access
    the entries in the Tree randomly and your Tree is in split mode.

 Build the optional branch supporting the TRefTable.
 This branch will keep all the information to find the branches
 containing referenced objects.

 At each Tree::Fill, the branch numbers containing the
 referenced objects are saved to the TBranchRef basket.
 When the Tree header is saved (via TTree::Write), the branch
 is saved keeping the information with the pointers to the branches
 having referenced objects.

 Create a new TTree BranchElement.

    WARNING about this new function


    This function is designed to replace the internal
    implementation of the old TTree::Branch (whose implementation
    has been moved to BranchOld).

    NOTE: The 'Bronch' method supports only one possible calls
    signature (where the object type has to be specified
    explicitly and the address must be the address of a pointer).
    For more flexibility use 'Branch'.  Use Bronch only in (rare)
    cases (likely to be legacy cases) where both the new and old
    implementation of Branch needs to be used at the same time.

    This function is far more powerful than the old Branch
    function.  It supports the full C++, including STL and has
    the same behaviour in split or non-split mode. classname does
    not have to derive from TObject.  The function is based on
    the new TStreamerInfo.

    Build a TBranchElement for an object of class classname.

    addr is the address of a pointer to an object of class
    classname.  The class dictionary must be available (ClassDef
    in class header).

    Note: See the comments in TBranchElement::SetAddress() for a more
          detailed discussion of the meaning of the addr parameter.

    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.

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

      IMPORTANT NOTE about branch names
    In case two or more master branches contain subbranches with
    identical names, one must add a "." (dot) character at the end
    of the master branch name. This will force the name of the subbranch
    to be master.subbranch instead of simply subbranch.
    This situation happens when the top level object (say event)
    has two or more members referencing the same class.
    For example, if a Tree has two branches B1 and B2 corresponding
    to objects of the same class MyClass, one can do:
       tree.Branch("B1.","MyClass",&b1,8000,1);
       tree.Branch("B2.","MyClass",&b2,8000,1);
    if MyClass has 3 members a,b,c, the two instructions above will generate
    subbranches called B1.a, B1.b ,B1.c, B2.a, B2.b, B2.c

    bufsize is the buffer size in bytes for this branch
    The default value is 32000 bytes and should be ok for most cases.
    You can specify a larger value (e.g. 256000) if your Tree is not split
    and each entry is large (Megabytes)
    A small value for bufsize is optimum if you intend to access
    the entries in the Tree randomly and your Tree is in split mode.

    Use splitlevel < 0 instead of splitlevel=0 when the class
    has a custom Streamer

    Note: if the split level is set to the default (99),  TTree::Branch will
    not issue a warning if the class can not be split.

 Helper function implementing TTree::Bronch and TTree::Branch(const char *name, T &obj);

 Browse content of the TTree.

 Build a Tree Index (default is TTreeIndex).
 See a description of the parameters and functionality in
 TTreeIndex::TTreeIndex().

 The return value is the number of entries in the Index (< 0 indicates failure).

 A TTreeIndex object pointed by fTreeIndex is created.
 This object will be automatically deleted by the TTree destructor.
 See also comments in TTree::SetTreeIndex().

 Build StreamerInfo for class cl.
 pointer is an optional argument that may contain a pointer to an object of cl.

 Called by TTree::Fill() when file has reached its maximum fgMaxTreeSize.
 Create a new file. If the original file is named "myfile.root",
 subsequent files are named "myfile_1.root", "myfile_2.root", etc.

 Returns a pointer to the new file.

 Currently, the automatic change of file is restricted
 to the case where the tree is in the top level directory.
 The file should not contain sub-directories.

 Before switching to a new file, the tree header is written
 to the current file, then the current file is closed.

 To process the multiple files created by ChangeFile, one must use
 a TChain.

 The new file name has a suffix "_N" where N is equal to fFileNumber+1.
 By default a Root session starts with fFileNumber=0. One can set
 fFileNumber to a different value via TTree::SetFileNumber.
 In case a file named "_N" already exists, the function will try
 a file named "__N", then "___N", etc.

 fgMaxTreeSize can be set via the static function TTree::SetMaxTreeSize.
 The default value of fgMaxTreeSize is 100 Gigabytes.

 If the current file contains other objects like TH1 and TTree,
 these objects are automatically moved to the new file.

 IMPORTANT NOTE:
 Be careful when writing the final Tree header to the file!
 Don't do:
  TFile *file = new TFile("myfile.root","recreate");
  TTree *T = new TTree("T","title");
  T->Fill(); //loop
  file->Write();
  file->Close();
 but do the following:
  TFile *file = new TFile("myfile.root","recreate");
  TTree *T = new TTree("T","title");
  T->Fill(); //loop
  file = T->GetCurrentFile(); //to get the pointer to the current file
  file->Write();
  file->Close();

 Check whether or not the address described by the last 3 parameters
 matches the content of the branch. If a Data Model Evolution conversion
 is involved, reset the fInfo of the branch.
 The return values are:
  kMissingBranch (-5) : Missing branch
  kInternalError (-4) : Internal error (could not find the type corresponding to a data type number)
  kMissingCompiledCollectionProxy (-3) : Missing compiled collection proxy for a compiled collection
  kMismatch (-2) : Non-Class Pointer type given does not match the type expected by the branch
  kClassMismatch (-1) : Class Pointer type given does not match the type expected by the branch
  kMatch (0) : perfect match
  kMatchConversion (1) : match with (I/O) conversion
  kMatchConversionCollection (2) : match with (I/O) conversion of the content of a collection
  kMakeClass (3) : MakeClass mode so we can not check.
  kVoidPtr (4) : void* passed so no check was made.
  kNoCheck (5) : Underlying TBranch not yet available so no check was made.

 Create a clone of this tree and copy nentries.

 By default copy all entries.
 The compression level of the cloned tree is set to the destination
 file's compression level.

 NOTE: Only active branches are copied.
 NOTE: If the TTree is a TChain, the structure of the first TTree
       is used for the copy.

 IMPORTANT: The cloned tree stays connected with this tree until
            this tree is deleted. In particular, any changes in
            branch addresses in this tree are forwarded to the
            clone trees, unless a branch in a clone tree has had
            its address changed, in which case that change stays in
            effect. When this tree is deleted, all the addresses of
            the cloned tree are reset to their default values.

 If 'option' contains the word 'fast' and nentries is -1, the
 cloning will be done without unzipping or unstreaming the baskets
 (i.e., a direct copy of the raw bytes on disk).

 When 'fast' is specified, 'option' can also contain a sorting
 order for the baskets in the output file.

 There are currently 3 supported sorting order:
    SortBasketsByOffset (the default)
    SortBasketsByBranch
    SortBasketsByEntry

 When using SortBasketsByOffset the baskets are written in the
 output file in the same order as in the original file (i.e. the
 baskets are sorted by their offset in the original file; Usually
 this also means that the baskets are sorted by the index/number of
 the _last_ entry they contain)

 When using SortBasketsByBranch all the baskets of each individual
 branches are stored contiguously. This tends to optimize reading
 speed when reading a small number (1->5) of branches, since all
 their baskets will be clustered together instead of being spread
 across the file. However it might decrease the performance when
 reading more branches (or the full entry).

 When using SortBasketsByEntry the baskets with the lowest starting
 entry are written first. (i.e. the baskets are sorted by the
 index/number of the first entry they contain). This means that on
 the file the baskets will be in the order in which they will be
 needed when reading the whole tree sequentially.

 For examples of CloneTree, see tutorials:

  -- copytree

     A macro to copy a subset of a TTree to a new TTree.

     The input file has been generated by the program in
     $ROOTSYS/test/Event with: Event 1000 1 1 1

  -- copytree2

     A macro to copy a subset of a TTree to a new TTree.

     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

 Set branch addresses of passed tree equal to ours.
 If undo is true, reset the branch address instead of copying them.
    This insures 'separation' of a cloned tree from its original

 Copy nentries from given tree to this tree.
 This routines assumes that the branches that intended to be copied are
 already connected.   The typical case is that this tree was created using
 tree->CloneTree(0).

 By default copy all entries.

 Returns number of bytes copied to this tree.

 If 'option' contains the word 'fast' and nentries is -1, the cloning will be
 done without unzipping or unstreaming the baskets (i.e., a direct copy of the
 raw bytes on disk).

 When 'fast' is specified, 'option' can also contains a sorting order for the
 baskets in the output file.

 There are currently 3 supported sorting order:
    SortBasketsByOffset (the default)
    SortBasketsByBranch
    SortBasketsByEntry

 See TTree::CloneTree for a detailed explanation of the semantics of these 3 options.

 If the tree or any of the underlying tree of the chain has an index, that index and any
 index in the subsequent underlying TTree objects will be merged.

 There are currently three 'options' to control this merging:
    NoIndex             : all the TTreeIndex object are dropped.
    DropIndexOnError    : if any of the underlying TTree object do no have a TTreeIndex,
                          they are all dropped.
    AsIsIndexOnError [default]: In case of missing TTreeIndex, the resulting TTree index has gaps.
    BuildIndexOnError : If any of the underlying TTree objects do not have a TTreeIndex,
                          all TTreeIndex are 'ignored' and the missing piece are rebuilt.

 Copy a tree with selection.

 IMPORTANT:

   The returned copied tree stays connected with the original tree
   until the original tree is deleted.  In particular, any changes
   to the branch addresses in the original tree are also made to
   the copied tree.  Any changes made to the branch addresses of the
   copied tree are overridden anytime the original tree changes its
   branch addresses.  When the original tree is deleted, all the
   branch addresses of the copied tree are set to zero.

 For examples of CopyTree, see the tutorials:

 copytree

 Example macro to copy a subset of a tree to a new tree.

 The input file was generated by running the program in
 $ROOTSYS/test/Event in this way:

      ./Event 1000 1 1 1

 copytree2

 Example 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 was generated by running the program in
 $ROOTSYS/test/Event in this way:

      ./Event 1000 1 1 1

 copytree3

 Example macro to copy a subset of a tree to a new tree.

 Only selected entries are copied to the new tree.
 NOTE that only the active branches are copied.

 Create a basket for this tree and given branch.

 Delete this tree from memory or/and disk.

  if option == "all" delete Tree object from memory AND from disk
                     all baskets on disk are deleted. All keys with same name
                     are deleted.
  if option =="" only Tree object in memory is deleted.

 Called by TKey and TObject::Clone to automatically add us to a directory
 when we are read from a file.

 Draw expression varexp for specified entries.
 Returns -1 in case of error or number of selected events in case of success.

      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.
 Returns -1 in case of error or number of selected events in case of success.

  varexp is an expression of the general form
   - "e1"           produces a 1-d histogram (TH1F) of expression "e1"
   - "e1:e2"        produces an unbinned 2-d scatter-plot (TGraph) of "e1"
                    on the y-axis versus "e2" on the x-axis
   - "e1:e2:e3"     produces an unbinned 3-d scatter-plot (TPolyMarker3D) of "e1"
                    versus "e2" versus "e3" on the x-, y-, z-axis, respectively.
   - "e1:e2:e3:e4"  produces an unbinned 3-d scatter-plot (TPolyMarker3D) of "e1"
                    versus "e2" versus "e3" and "e4" mapped on the color number.
  (to create histograms in the 2, 3, and 4 dimensional case, see section "Saving
  the result of Draw to an histogram")

  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 distribution of y versus sqrt(x)
            = px:py:pz:2.5*E  produces a 3-d scatter-plot of px vs py ps pz
              and the color number of each marker will be 2.5*E.
              If the color number is negative it is set to 0.
              If the color number is greater than the current number of colors
                 it is set to the highest color number.
              The default number of colors is 50.
              see TStyle::SetPalette for setting a new color palette.

  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.

  The expressions can use all the operations and build-in functions
  supported by TFormula (See TFormula::Analyze), including free
  standing function taking numerical arguments (TMath::Bessel).
  In addition, you can call member functions taking numerical
  arguments. For example:
      - "TMath::BreitWigner(fPx,3,2)"
      - "event.GetHistogram().GetXaxis().GetXmax()"
  Note: You can only pass expression that depend on the TTree's data
  to static functions and you can only call non-static member function
  with 'fixed' parameters.

  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 weight = 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 COL is specified when varexp has three fields:
            tree.Draw("e1:e2:e3","","col");
      a 2D scatter is produced with e1 vs e2, and e3 is mapped on the color
      table. The colors for e3 are evaluated once in linear scale before
      painting. Therefore changing the pad to log scale along Z as no effect
      on the colors.
    - 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)

  This function returns the number of selected entries. It returns -1
  if an error occurs.

     Drawing expressions using arrays and array elements

 Let assumes, a leaf fMatrix, on the branch fEvent, which is a 3 by 3 array,
 or a TClonesArray.
 In a TTree::Draw expression you can now access fMatrix using the following
 syntaxes:

   String passed    What is used for each entry of the tree

   "fMatrix"       the 9 elements of fMatrix
   "fMatrix[][]"   the 9 elements of fMatrix
   "fMatrix[2][2]" only the elements fMatrix[2][2]
   "fMatrix[1]"    the 3 elements fMatrix[1][0], fMatrix[1][1] and fMatrix[1][2]
   "fMatrix[1][]"  the 3 elements fMatrix[1][0], fMatrix[1][1] and fMatrix[1][2]
   "fMatrix[][0]"  the 3 elements fMatrix[0][0], fMatrix[1][0] and fMatrix[2][0]

   "fEvent.fMatrix...." same as "fMatrix..." (unless there is more than one leaf named fMatrix!).

 In summary, if a specific index is not specified for a dimension, TTree::Draw
 will loop through all the indices along this dimension.  Leaving off the
 last (right most) dimension of specifying then with the two characters '[]'
 is equivalent.  For variable size arrays (and TClonesArray) the range
 of the first dimension is recalculated for each entry of the tree.
 You can also specify the index as an expression of any other variables from the
 tree.

 TTree::Draw also now properly handling operations involving 2 or more arrays.

 Let assume a second matrix fResults[5][2], here are a sample of some
 of the possible combinations, the number of elements they produce and
 the loop used:

  expression                       element(s)  Loop

  "fMatrix[2][1] - fResults[5][2]"   one     no loop
  "fMatrix[2][]  - fResults[5][2]"   three   on 2nd dim fMatrix
  "fMatrix[2][]  - fResults[5][]"    two     on both 2nd dimensions
  "fMatrix[][2]  - fResults[][1]"    three   on both 1st dimensions
  "fMatrix[][2]  - fResults[][]"     six     on both 1st and 2nd dimensions of
                                             fResults
  "fMatrix[][2]  - fResults[3][]"    two     on 1st dim of fMatrix and 2nd of
                                             fResults (at the same time)
  "fMatrix[][]   - fResults[][]"     six     on 1st dim then on  2nd dim

  "fMatrix[][fResult[][]]"           30      on 1st dim of fMatrix then on both
                                             dimensions of fResults.  The value
                                             if fResults[j][k] is used as the second
                                             index of fMatrix.


 In summary, TTree::Draw loops through all unspecified dimensions.  To
 figure out the range of each loop, we match each unspecified dimension
 from left to right (ignoring ALL dimensions for which an index has been
 specified), in the equivalent loop matched dimensions use the same index
 and are restricted to the smallest range (of only the matched dimensions).
 When involving variable arrays, the range can of course be different
 for each entry of the tree.

 So the loop equivalent to "fMatrix[][2] - fResults[3][]" is:

    for (Int_t i0; i < min(3,2); i++) {
       use the value of (fMatrix[i0][2] - fMatrix[3][i0])
    }

 So the loop equivalent to "fMatrix[][2] - fResults[][]" is:

    for (Int_t i0; i < min(3,5); i++) {
       for (Int_t i1; i1 < 2; i1++) {
          use the value of (fMatrix[i0][2] - fMatrix[i0][i1])
       }
    }

 So the loop equivalent to "fMatrix[][] - fResults[][]" is:

    for (Int_t i0; i < min(3,5); i++) {
       for (Int_t i1; i1 < min(3,2); i1++) {
          use the value of (fMatrix[i0][i1] - fMatrix[i0][i1])
       }
    }

 So the loop equivalent to "fMatrix[][fResults[][]]" is:

    for (Int_t i0; i0 < 3; i0++) {
       for (Int_t j2; j2 < 5; j2++) {
          for (Int_t j3; j3 < 2; j3++) {
             i1 = fResults[j2][j3];
             use the value of fMatrix[i0][i1]
       }
    }

     Retrieving the result of Draw


  By default the temporary histogram created is called "htemp", but only in
  the one dimensional Draw("e1") it contains the TTree's data points. For
  a two dimensional Draw, the data is filled into a TGraph which is named
  "Graph". They can be retrieved by calling
    TH1F *htemp = (TH1F*)gPad->GetPrimitive("htemp"); // 1D
    TGraph *graph = (TGraph*)gPad->GetPrimitive("Graph"); // 2D

  For a three and four dimensional Draw the TPolyMarker3D is unnamed, and
  cannot be retrieved.

  gPad always contains a TH1 derived object called "htemp" which allows to
  access the axes:
    TGraph *graph = (TGraph*)gPad->GetPrimitive("Graph"); // 2D
    TH2F   *htemp = (TH2F*)gPad->GetPrimitive("htemp"); // empty, but has axes
    TAxis  *xaxis = htemp->GetXaxis();

     Saving the result of Draw to an histogram


  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 (and also the current pad). This works for all dimensions.
  Example:
    tree.Draw("sqrt(x)>>hsqrt","y>0")
    will draw sqrt(x) and save the histogram as "hsqrt" in the current
    directory.  To retrieve it do:
    TH1F *hsqrt = (TH1F*)gDirectory->Get("hsqrt");

  The binning information is taken from the environment variables

     Hist.Binning.?D.?

  In addition, the name of the histogram can be followed by up to 9
  numbers between '(' and ')', where the numbers describe the
  following:

   1 - bins in x-direction
   2 - lower limit in x-direction
   3 - upper limit in x-direction
   4-6 same for y-direction
   7-9 same for z-direction

   When a new binning is used the new value will become the default.
   Values can be skipped.
  Example:
    tree.Draw("sqrt(x)>>hsqrt(500,10,20)")
          // plot sqrt(x) between 10 and 20 using 500 bins
    tree.Draw("sqrt(x):sin(y)>>hsqrt(100,10,60,50,.1,.5)")
          // plot sqrt(x) against sin(y)
          // 100 bins in x-direction; lower limit on x-axis is 10; upper limit is 60
          //  50 bins in y-direction; lower limit on y-axis is .1; upper limit is .5

  By default, the specified histogram is reset.
  To continue to append data to an existing histogram, use "+" in front
  of the histogram name.
  A '+' in front of the histogram name is ignored, when the name is followed by
  binning information as described in the previous paragraph.
    tree.Draw("sqrt(x)>>+hsqrt","y>0")
      will not reset hsqrt, but will continue filling.
  This works for 1-D, 2-D and 3-D histograms.

     Accessing collection objects


  TTree::Draw default's handling of collections is to assume that any
  request on a collection pertain to it content.  For example, if fTracks
  is a collection of Track objects, the following:
      tree->Draw("event.fTracks.fPx");
  will plot the value of fPx for each Track objects inside the collection.
  Also
     tree->Draw("event.fTracks.size()");
  would plot the result of the member function Track::size() for each
  Track object inside the collection.
  To access information about the collection itself, TTree::Draw support
  the '@' notation.  If a variable which points to a collection is prefixed
  or postfixed with '@', the next part of the expression will pertain to
  the collection object.  For example:
     tree->Draw("event.@fTracks.size()");
  will plot the size of the collection referred to by fTracks (i.e the number
  of Track objects).

     Drawing 'objects'


  When a class has a member function named AsDouble or AsString, requesting
  to directly draw the object will imply a call to one of the 2 functions.
  If both AsDouble and AsString are present, AsDouble will be used.
  AsString can return either a char*, a std::string or a TString.s
  For example, the following
     tree->Draw("event.myTTimeStamp");
  will draw the same histogram as
     tree->Draw("event.myTTimeStamp.AsDouble()");
  In addition, when the object is a type TString or std::string, TTree::Draw
  will call respectively TString::Data and std::string::c_str()

  If the object is a TBits, the histogram will contain the index of the bit
  that are turned on.

     Retrieving  information about the tree itself.


  You can refer to the tree (or chain) containing the data by using the
  string 'This'.
  You can then could any TTree methods.  For example:
     tree->Draw("This->GetReadEntry()");
  will display the local entry numbers be read.
     tree->Draw("This->GetUserInfo()->At(0)->GetName()");
  will display the name of the first 'user info' object.

     Special functions and variables


  Entry$:  A TTree::Draw formula can use the special variable Entry$
  to access the entry number being read.  For example to draw every
  other entry use:
    tree.Draw("myvar","Entry$%2==0");

  Entry$      : return the current entry number (== TTree::GetReadEntry())
  LocalEntry$ : return the current entry number in the current tree of a
                chain (== GetTree()->GetReadEntry())
  Entries$    : return the total number of entries (== TTree::GetEntries())
  Length$     : return the total number of element of this formula for this
                 entry (==TTreeFormula::GetNdata())
  Iteration$: return the current iteration over this formula for this
                 entry (i.e. varies from 0 to Length$).

  Length$(formula): return the total number of element of the formula given as a
                    parameter.
  Sum$(formula): return the sum of the value of the elements of the formula given
                    as a parameter.  For example the mean for all the elements in
                    one entry can be calculated with:
                Sum$(formula)/Length$(formula)
  Min$(formula): return the minimun (within one TTree entry) of the value of the
                    elements of the formula given as a parameter.
  Max$(formula): return the maximum (within one TTree entry) of the value of the
                    elements of the formula given as a parameter.
  MinIf$(formula,condition)
  MaxIf$(formula,condition): return the minimum (maximum) (within one TTree entry)
                    of the value of the elements of the formula given as a parameter
                    if they match the condition. If no element matches the condition,
                    the result is zero.  To avoid the resulting peak at zero, use the
                    pattern:
    tree->Draw("MinIf$(formula,condition)","condition");
                    which will avoid calculation MinIf$ for the entries that have no match
                    for the condition.

  Alt$(primary,alternate) : return the value of "primary" if it is available
                 for the current iteration otherwise return the value of "alternate".
                 For example, with arr1[3] and arr2[2]
    tree->Draw("arr1+Alt$(arr2,0)");
                 will draw arr1[0]+arr2[0] ; arr1[1]+arr2[1] and arr1[2]+0
                 Or with a variable size array arr3
    tree->Draw("Alt$(arr3[0],0)+Alt$(arr3[1],0)+Alt$(arr3[2],0)");
                 will draw the sum arr3 for the index 0 to min(2,actual_size_of_arr3-1)
                 As a comparison
    tree->Draw("arr3[0]+arr3[1]+arr3[2]");
                 will draw the sum arr3 for the index 0 to 2 only if the
                 actual_size_of_arr3 is greater or equal to 3.
                 Note that the array in 'primary' is flattened/linearized thus using
                 Alt$ with multi-dimensional arrays of different dimensions in unlikely
                 to yield the expected results.  To visualize a bit more what elements
                 would be matched by TTree::Draw, TTree::Scan can be used:
    tree->Scan("arr1:Alt$(arr2,0)");
                 will print on one line the value of arr1 and (arr2,0) that will be
                 matched by
    tree->Draw("arr1-Alt$(arr2,0)");

  The ternary operator is not directly supported in TTree::Draw however, to plot the
  equivalent of 'var2<20 ? -99 : var1', you can use:
     tree->Draw("(var2<20)*99+(var2>=20)*var1","");

     Drawing a user function accessing the TTree data directly


  If the formula contains  a file name, TTree::MakeProxy will be used
  to load and execute this file.   In particular it will draw the
  result of a function with the same name as the file.  The function
  will be executed in a context where the name of the branches can
  be used as a C++ variable.

  For example draw px using the file hsimple.root (generated by the
  hsimple.C tutorial), we need a file named hsimple.cxx:

     double hsimple() {
        return px;
     }

  MakeProxy can then be used indirectly via the TTree::Draw interface
  as follow:
     new TFile("hsimple.root")
     ntuple->Draw("hsimple.cxx");

  A more complete example is available in the tutorials directory:
    h1analysisProxy.cxx , h1analysProxy.h and h1analysisProxyCut.C
  which reimplement the selector found in h1analysis.C

  The main features of this facility are:

    * on-demand loading of branches
    * ability to use the 'branchname' as if it was a data member
    * protection against array out-of-bound
    * ability to use the branch data as object (when the user code is available)

  See TTree::MakeProxy for more details.

     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
  or option=profi or option=profg ; the trailing letter select the way
  the bin error are computed, See TProfile2D::SetErrorOption for
  details on the differences.
  The option=prof is automatically selected in case of y:x>>pf
  where pf is an existing TProfile histogram.

     Making a 2D Profile histogram

  In case of a 3-Dim expression, one can generate a TProfile2D histogram
  instead of a TH3F histogram by specifying option=prof or option=profs.
  or option=profi or option=profg ; the trailing letter select the way
  the bin error are computed, See TProfile2D::SetErrorOption for
  details on the differences.
  The option=prof is automatically selected in case of z:y:x>>pf
  where pf is an existing TProfile2D histogram.

     Making a 5D plot using GL

  If option GL5D is specified together with 5 variables, a 5D plot is drawn
  using OpenGL. See $ROOTSYS/tutorials/tree/staff.C as example.

     Making a parallel coordinates plot

  In case of a 2-Dim or more expression with the option=para, one can generate
  a parallel coordinates plot. With that option, the number of dimensions is
  arbitrary. Giving more than 4 variables without the option=para or
  option=candle or option=goff will produce an error.

     Making a candle sticks chart

  In case of a 2-Dim or more expression with the option=candle, one can generate
  a candle sticks chart. With that option, the number of dimensions is
  arbitrary. Giving more than 4 variables without the option=para or
  option=candle or option=goff will produce an error.

     Normalizing the output histogram to 1

  When option contains "norm" the output histogram is normalized to 1.

     Saving the result of Draw to a TEventList, a TEntryList or a TEntryListArray

  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.
  If option "entrylist" is used, a TEntryList object is created
  If the selection contains arrays, vectors or any container class and option
  "entrylistarray" is used, a TEntryListArray object is created
  containing also the subentries satisfying the selection, i.e. the indices of
  the branches which hold containers classes.
  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.
    tree.Draw(">>yplus", "y>0", "entrylist")
    will create a TEntryList object names "yplus" in the current directory
    tree.Draw(">>yplus", "y>0", "entrylistarray")
    will create a TEntryListArray object names "yplus" in the current directory

  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, TEntryList or TEntryListArray as Input

  Once a TEventList or a TEntryList object has been generated, it can be used as input
  for TTree::Draw. Use TTree::SetEventList or TTree::SetEntryList to set the
  current event list
  Example1:
     TEventList *elist = (TEventList*)gDirectory->Get("yplus");
     tree->SetEventList(elist);
     tree->Draw("py");
  Example2:
     TEntryList *elist = (TEntryList*)gDirectory->Get("yplus");
     tree->SetEntryList(elist);
     tree->Draw("py");
  If a TEventList object is used as input, a new TEntryList object is created
  inside the SetEventList function. In case of a TChain, all tree headers are loaded
  for this transformation. This new object is owned by the chain and is deleted
  with it, unless the user extracts it by calling GetEntryList() function.
  See also comments to SetEventList() function of TTree and TChain.

  If arrays are used in the selection criteria and TEntryListArray is not used,
  all the entries that have at least one element of the array that satisfy the selection
  are entered in the list.
  Example:
      tree.Draw(">>pyplus","fTracks.fPy>0");
      tree->SetEventList(pyplus);
      tree->Draw("fTracks.fPy");
  will draw the fPy of ALL tracks in event with at least one track with
  a positive fPy.

  To select only the elements that did match the original selection
  use TEventList::SetReapplyCut or TEntryList::SetReapplyCut.
  Example:
      tree.Draw(">>pyplus","fTracks.fPy>0");
      pyplus->SetReapplyCut(kTRUE);
      tree->SetEventList(pyplus);
      tree->Draw("fTracks.fPy");
  will draw the fPy of only the tracks that have a positive fPy.

  To draw only the elements that match a selection in case of arrays,
  you can also use TEntryListArray (faster in case of a more general selection).
  Example:
      tree.Draw(">>pyplus","fTracks.fPy>0", "entrylistarray");
      tree->SetEntryList(pyplus);
      tree->Draw("fTracks.fPy");

  will draw the fPy of only the tracks that have a positive fPy,
  but without redoing the selection.

  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 values accepted by the
                          //selection expression. In case where no selection
                          //was specified, returns the number of values processed.
    -GetV1()              //returns a pointer to the double array of V1
    -GetV2()              //returns a pointer to the double array of V2
    -GetV3()              //returns a pointer to the double array of V3
    -GetV4()              //returns a pointer to the double array of V4
    -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:V4",selection);
   If the expression has more than 4 component use GetVal(index)

   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 GetW, GetV1, GetV2, GetV3, GetV4, GetVal with a length corresponding
    to the parameter fEstimate.  The content will be the last
            GetSelectedRows() % GetEstimate()
    values calculated.
    By default fEstimate=1000000 and can be modified
    via TTree::SetEstimate. To keep in memory all the results (in case
    where there is only one result per entry), use
       tree->SetEstimate(tree->GetEntries()+1); // same as tree->SetEstimate(-1);
    You must call SetEstimate if the expected number of selected rows
    you need to look at is greater than 1000000.

    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();"

 Remove some baskets from memory.

 Drop branch buffers to accommodate nbytes below MaxVirtualsize.

 Fill all branches.

   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.

   This machine independent version of the data is copied into a
   basket (each branch has its own basket).  When a basket is full
   (32k worth of data by default), it is then optionally compressed
   and written to disk (this operation is also called committing or
   'flushing' the basket).  The committed baskets are then
   immediately removed from memory.

   The function returns the number of bytes committed to the
   individual branches.

   If a write error occurs, the number of bytes returned is -1.

   If no data are written, because, e.g., the branch is disabled,
   the number of bytes returned is 0.

        The baskets are flushed and the Tree header saved at regular intervals

   At regular intervals, when the amount of data written so far is
   greater than fAutoFlush (see SetAutoFlush) all the baskets are flushed to disk.
   This makes future reading faster as it guarantees that baskets belonging to nearby
   entries will be on the same disk region.
   When the first call to flush the baskets happen, we also take this opportunity
   to optimize the baskets buffers.
   We also check if the amount of data written is greater than fAutoSave (see SetAutoSave).
   In this case we also write the Tree header. This makes the Tree recoverable up to this point
   in case the program writing the Tree crashes.
   The decisions to FlushBaskets and Auto Save can be made based either on the number
   of bytes written (fAutoFlush and fAutoSave negative) or on the number of entries
   written (fAutoFlush and fAutoSave positive).
   Note that the user can decide to call FlushBaskets and AutoSave in her event loop
   base on the number of events written instead of the number of bytes written.

   Note that calling FlushBaskets too often increases the IO time.
   Note that calling AutoSave too often increases the IO time and also the file size.

 Return the branch that correspond to the path 'branchname', which can
 include the name of the tree or the omitted name of the parent branches.
 In case of ambiguity, returns the first match.

 FIXME: Describe this function.

 Fit  a projected item(s) from a tree.

  funcname is a TF1 function.

  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.

  The function returns the number of selected entries.

  Example:
    tree.Fit(pol4,sqrt(x)>>hsqrt,y>0)
    will fit sqrt(x) and save the histogram as "hsqrt" in the current
    directory.

   See also TTree::UnbinnedFit

   Return status

  The function returns the status of the histogram fit (see TH1::Fit)
  If no entries were selected, the function returns -1;
   (i.e. fitResult is null is the fit is OK)

 Write to disk all the basket that have not yet been individually written.

 Return the number of bytes written or -1 in case of write error.

 Returns the expanded value of the alias.  Search in the friends if any.

 Return pointer to the branch with the given name in this tree or its friends.

 Return status of branch with name branchname.
 0 if branch is not activated
 1 if branch is activated

 Static function returning the current branch style.
 style = 0 old Branch
 style = 1 new Bronch

 Used for automatic sizing of the cache.
 Estimates a suitable size for the tree cache based on AutoFlush.
 A cache sizing factor is taken from the configuration. If this yields zero
 and withDefault is true the historical algoirthm for default size is used.

 Return pointer to the current file.

 Return the number of entries matching the selection.
 Return -1 in case of errors.

 If the selection uses any arrays or containers, we return the number
 of entries where at least one element match the selection.
 GetEntries is implemented using the selector class TSelectorEntries,
 which can be used directly (see code in TTreePlayer::GetEntries) for
 additional option.
 If SetEventList was used on the TTree or TChain, only that subset
 of entries will be considered.

 Return pointer to the 1st Leaf named name in any Branch of this Tree or
 any branch in the list of friend trees.

 Read all branches of entry and return total number of bytes read.

     getall = 0 : get only active branches
     getall = 1 : get all branches

  The function returns the number of bytes read from the input buffer.
  If entry does not exist the function returns 0.
  If an I/O error occurs, the function returns -1.

  If the Tree has friends, also read the friends entry.

  To activate/deactivate one or more branches, use TBranch::SetBranchStatus
  For example, if you have a Tree with several hundred branches, and you
  are interested only by branches named "a" and "b", do
     mytree.SetBranchStatus("*",0); //disable all branches
     mytree.SetBranchStatus("a",1);
     mytree.SetBranchStatus("b",1);
  when calling mytree.GetEntry(i); only branches "a" and "b" will be read.

  WARNING!!
  If your Tree has been created in split mode with a parent branch "parent.",
     mytree.SetBranchStatus("parent",1);
  will not activate the sub-branches of "parent". You should do:
     mytree.SetBranchStatus("parent*",1);

  Without the trailing dot in the branch creation you have no choice but to
  call SetBranchStatus explicitly for each of the sub branches.

  An alternative is to call directly
     brancha.GetEntry(i)
     branchb.GetEntry(i);

  IMPORTANT NOTE

 By default, GetEntry reuses the space allocated by the previous object
 for each branch. You can force the previous object to be automatically
 deleted if you call mybranch.SetAutoDelete(kTRUE) (default is kFALSE).
 Example:
 Consider the example in $ROOTSYS/test/Event.h
 The top level branch in the tree T is declared with:
    Event *event = 0;  //event must be null or point to a valid object
                       //it must be initialized
    T.SetBranchAddress("event",&event);
 When reading the Tree, one can choose one of these 3 options:

   OPTION 1


    for (Long64_t i=0;i<nentries;i++) {
       T.GetEntry(i);
       // the object event has been filled at this point
    }
   The default (recommended). At the first entry an object of the class
   Event will be created and pointed by event. At the following entries,
   event will be overwritten by the new data. All internal members that are
   TObject* are automatically deleted. It is important that these members
   be in a valid state when GetEntry is called. Pointers must be correctly
   initialized. However these internal members will not be deleted if the
   characters "->" are specified as the first characters in the comment
   field of the data member declaration.

   If "->" is specified, the pointer member is read via pointer->Streamer(buf).
   In this case, it is assumed that the pointer is never null (case of
   pointer TClonesArray *fTracks in the Event example). If "->" is not
   specified, the pointer member is read via buf >> pointer. In this case
   the pointer may be null. Note that the option with "->" is faster to
   read or write and it also consumes less space in the file.

   OPTION 2

  The option AutoDelete is set
   TBranch *branch = T.GetBranch("event");
   branch->SetAddress(&event);
   branch->SetAutoDelete(kTRUE);
    for (Long64_t i=0;i<nentries;i++) {
       T.GetEntry(i);
       // the object event has been filled at this point
    }
   In this case, at each iteration, the object event is deleted by GetEntry
   and a new instance of Event is created and filled.

   OPTION 3

   Same as option 1, but you delete yourself the event.
    for (Long64_t i=0;i<nentries;i++) {
       delete event;
       event = 0;  // EXTREMELY IMPORTANT
       T.GetEntry(i);
       // the object event has been filled at this point
    }

  It is strongly recommended to use the default option 1. It has the
  additional advantage that functions like TTree::Draw (internally calling
  TTree::GetEntry) will be functional even when the classes in the file are
  not available.

  Note: See the comments in TBranchElement::SetAddress() for the
    object ownership policy of the underlying (user) data.

Returns the entry list, set to this tree

 Return entry number corresponding to entry.

 if no TEntryList set returns entry
 else returns the entry number corresponding to the list index=entry

 Return entry number corresponding to major and minor number.
 Note that this function returns only the entry number, not the data
 To read the data corresponding to an entry number, use TTree::GetEntryWithIndex
 the BuildIndex function has created a table of Long64_t* of sorted values
 corresponding to val = major<<31 + minor;
 The function performs binary search in this sorted table.
 If it finds a pair that maches val, it returns directly the
 index in the table.
 If an entry corresponding to major and minor is not found, the function
 returns the index of the major,minor pair immediately lower than the
 requested value, ie it will return -1 if the pair is lower than
 the first entry in the index.

 See also GetEntryNumberWithIndex

 Return entry number corresponding to major and minor number.
 Note that this function returns only the entry number, not the data
 To read the data corresponding to an entry number, use TTree::GetEntryWithIndex
 the BuildIndex function has created a table of Long64_t* of sorted values
 corresponding to val = major<<31 + minor;
 The function performs binary search in this sorted table.
 If it finds a pair that maches val, it returns directly the
 index in the table, otherwise it returns -1.

 See also GetEntryNumberWithBestIndex

 Read entry corresponding to major and minor number.

  The function returns the total number of bytes read.
  If the Tree has friend trees, the corresponding entry with
  the index values (major,minor) is read. Note that the master Tree
  and its friend may have different entry serial numbers corresponding
  to (major,minor).

 Return a pointer to the TTree friend whose name or alias is 'friendname.

 If the 'tree' is a friend, this method returns its alias name.

 This alias is an alternate name for the tree.

 It can be used in conjunction with a branch or leaf name in a TTreeFormula,
 to specify in which particular tree the branch or leaf can be found if
 the friend trees have branches or leaves with the same name as the master
 tree.

 It can also be used in conjunction with an alias created using
 TTree::SetAlias in a TTreeFormula, e.g.:

      maintree->Draw("treealias.fPx - treealias.myAlias");

 where fPx is a branch of the friend tree aliased as 'treealias' and 'myAlias'
 was created using TTree::SetAlias on the friend tree.

 However, note that 'treealias.myAlias' will be expanded literally,
 without remembering that it comes from the aliased friend and thus
 the branch name might not be disambiguated properly, which means
 that you may not be able to take advantage of this feature.

 Creates a new iterator that will go through all the leaves on the tree itself and its friend.

 Return pointer to the 1st Leaf named name in any Branch of this
 Tree or any branch in the list of friend trees.

 The leaf name can contain the name of a friend tree with the
 syntax: friend_dir_and_tree.full_leaf_name
 the friend_dir_and_tree can be of the form
    TDirectoryName/TreeName

 Return pointer to the 1st Leaf named name in any Branch of this
 Tree or any branch in the list of friend trees.

 The leaf name can contain the name of a friend tree with the
 syntax: friend_dir_and_tree.full_leaf_name
 the friend_dir_and_tree can be of the form
    TDirectoryName/TreeName

 Return pointer to the 1st Leaf named name in any Branch of this
 Tree or any branch in the list of friend trees.

 aname may be of the form branchname/leafname

 Return maximum of column with name columname.
 if the Tree has an associated TEventList or TEntryList, the maximum
 is computed for the entries in this list.

 Static function which returns the tree file size limit in bytes.

 Return minimum of column with name columname.
 if the Tree has an associated TEventList or TEntryList, the minimum
 is computed for the entries in this list.

 Load the TTreePlayer (if not already done).

 Find and return the TTreeCache registered with the file and which may
 contain branches for us. If create is true and there is no cache:
 Create a new cache according to the autocache setting and return it.

 Return a pointer to the list containing user objects associated to this tree.

 The list is automatically created if it does not exist.

 WARNING: By default the TTree destructor will delete all objects added
          to this list. If you do not want these objects to be deleted,
          call:

               mytree->GetUserInfo()->Clear();

          before deleting the tree.

 Appends the cluster range information stored in 'fromtree' to this tree,
 including the value of fAutoFlush.

 This is used when doing a fast cloning (by TTreeCloner).
 See also fAutoFlush and fAutoSave if needed.

 Keep a maximum of fMaxEntries in memory.

 Read in memory all baskets from all branches up to the limit of maxmemory bytes.

 If maxmemory is non null and positive SetMaxVirtualSize is called
 with this value. Default for maxmemory is 2000000000 (2 Gigabytes).
 The function returns the total number of baskets read into memory
 if negative an error occurred while loading the branches.
 This method may be called to force branch baskets in memory
 when random access to branch entries is required.
 If random access to only a few branches is required, you should
 call directly TBranch::LoadBaskets.

 Set current entry.

 Returns -2 if entry does not exist (just as TChain::LoadTree()).

 Note: This function is overloaded in TChain.

 Load entry on behalf of our master tree, we may use an index.

 Called by LoadTree() when the masterTree looks for the entry
 number in a friend tree (us) corresponding to the passed entry
 number in the masterTree.

 If we have no index, our entry number and the masterTree entry
 number are the same.

 If we *do* have an index, we must find the (major, minor) value pair
 in masterTree to locate our corresponding entry.

 Generate a skeleton analysis class for this tree.

 The following files are produced: classname.h and classname.C.
 If classname is 0, classname will be called "nameoftree".

 The generated code in classname.h includes the following:
    - Identification of the original tree and the input file name.
    - Definition of an analysis class (data members and member functions).
    - The following member functions:
       - constructor (by default opening the tree file),
       - GetEntry(Long64_t entry),
       - Init(TTree* tree) to initialize a new TTree,
       - Show(Long64_t entry) to read and dump entry.

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

 To use this function:
    - Open your tree file (eg: TFile f("myfile.root");)
    - T->MakeClass("MyClass");
 where T is the name of the TTree 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 = new MyClass;
    root > t->GetEntry(12); // Fill data members of t 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.

  NOTE: Do not use the code generated for a single TTree which is part
        of a TChain to process that entire TChain.  The maximum dimensions
        calculated for arrays on the basis of a single TTree from the TChain
        might be (will be!) too small when processing all of the TTrees in
        the TChain.  You must use myChain.MakeClass() to generate the code,
        not myTree.MakeClass(...).

 Generate a skeleton function for this tree.

 The function code is written on filename.
 If filename is 0, filename will be called nameoftree.C

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

 To use this function:
    - Open your Tree file (eg: TFile f("myfile.root");)
    - T->MakeCode("MyAnalysis.C");
 where T is the name of the TTree in file myfile.root
 and MyAnalysis.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 developed.

 Generate a skeleton analysis class for this Tree using TBranchProxy.

 TBranchProxy is the base of a class hierarchy implementing an
 indirect access to the content of the branches of a TTree.

 "proxyClassname" is expected to be of the form:
    [path/]fileprefix
 The skeleton will then be generated in the file:
    fileprefix.h
 located in the current directory or in 'path/' if it is specified.
 The class generated will be named 'fileprefix'

 "macrofilename" and optionally "cutfilename" are expected to point
 to source files which will be included by the generated skeleton.
 Method of the same name as the file(minus the extension and path)
 will be called by the generated skeleton's Process method as follow:
    [if (cutfilename())] htemp->Fill(macrofilename());

 "option" can be used select some of the optional features during
 the code generation.  The possible options are:
    nohist : indicates that the generated ProcessFill should not
             fill the histogram.

 'maxUnrolling' controls how deep in the class hierarchy does the
 system 'unroll' classes that are not split.  Unrolling a class
 allows direct access to its data members (this emulates the behavior
 of TTreeFormula).

 The main features of this skeleton are:

    * on-demand loading of branches
    * ability to use the 'branchname' as if it was a data member
    * protection against array out-of-bounds errors
    * ability to use the branch data as an object (when the user code is available)

 For example with Event.root, if
    Double_t somePx = fTracks.fPx[2];
 is executed by one of the method of the skeleton,
 somePx will updated with the current value of fPx of the 3rd track.

 Both macrofilename and the optional cutfilename are expected to be
 the name of source files which contain at least a free standing
 function with the signature:
     x_t macrofilename(); // i.e function with the same name as the file
 and
     y_t cutfilename();   // i.e function with the same name as the file

 x_t and y_t needs to be types that can convert respectively to a double
 and a bool (because the skeleton uses:
     if (cutfilename()) htemp->Fill(macrofilename());

 These two functions are run in a context such that the branch names are
 available as local variables of the correct (read-only) type.

 Note that if you use the same 'variable' twice, it is more efficient
 to 'cache' the value. For example
   Int_t n = fEventNumber; // Read fEventNumber
   if (n<10 || n>10) { ... }
 is more efficient than
   if (fEventNumber<10 || fEventNumber>10)

 Also, optionally, the generated selector will also call methods named
 macrofilename_methodname in each of 6 main selector methods if the method
 macrofilename_methodname exist (Where macrofilename is stripped of its
 extension).

 Concretely, with the script named h1analysisProxy.C,

 The method         calls the method (if it exist)
 Begin           -> void h1analysisProxy_Begin(TTree*);
 SlaveBegin      -> void h1analysisProxy_SlaveBegin(TTree*);
 Notify          -> Bool_t h1analysisProxy_Notify();
 Process         -> Bool_t h1analysisProxy_Process(Long64_t);
 SlaveTerminate  -> void h1analysisProxy_SlaveTerminate();
 Terminate       -> void h1analysisProxy_Terminate();

 If a file name macrofilename.h (or .hh, .hpp, .hxx, .hPP, .hXX) exist
 it is included before the declaration of the proxy class.  This can
 be used in particular to insure that the include files needed by
 the macro file are properly loaded.

 The default histogram is accessible via the variable named 'htemp'.

 If the library of the classes describing the data in the branch is
 loaded, the skeleton will add the needed #include statements and
 give the ability to access the object stored in the branches.

 To draw px using the file hsimple.root (generated by the
 hsimple.C tutorial), we need a file named hsimple.cxx:

     double hsimple() {
        return px;
     }

 MakeProxy can then be used indirectly via the TTree::Draw interface
 as follow:
     new TFile("hsimple.root")
     ntuple->Draw("hsimple.cxx");

 A more complete example is available in the tutorials directory:
   h1analysisProxy.cxx , h1analysProxy.h and h1analysisProxyCut.C
 which reimplement the selector found in h1analysis.C

 Generate skeleton selector class for this tree.

 The following files are produced: selector.h and selector.C.
 If selector is 0, the selector will be called "nameoftree".

 The generated code in selector.h includes the following:
    - Identification of the original Tree and Input file name
    - Definition of selector class (data and functions)
    - The following class functions:
       - constructor and destructor
       - void    Begin(TTree *tree)
       - void    SlaveBegin(TTree *tree)
       - void    Init(TTree *tree)
       - Bool_t  Notify()
       - Bool_t  Process(Long64_t entry)
       - void    Terminate()
       - void    SlaveTerminate()

 The class selector derives from TSelector.
 The generated code in selector.C includes empty functions defined above.

 To use this function:
    - connect your Tree file (eg: TFile f("myfile.root");)
    - T->MakeSelector("myselect");
 where T is the name of the Tree in file myfile.root
 and myselect.h, myselect.C the name of the files created by this function.
 In a ROOT session, you can do:
    root > T->Process("myselect.C")

 Check if adding nbytes to memory we are still below MaxVirtualsize.

 Static function merging the trees in the TList into a new tree.

 Trees in the list can be memory or disk-resident trees.
 The new tree is created in the current directory (memory if gROOT).

 Merge the trees in the TList into this tree.

 Returns the total number of entries in the merged tree.

 Merge the trees in the TList into this tree.
 If info->fIsFirst is true, first we clone this TTree info the directory
 info->fOutputDirectory and then overlay the new TTree information onto
 this TTree object (so that this TTree object is now the appropriate to
 use for further merging).

 Returns the total number of entries in the merged tree.

 Move a cache from a file to the current file in dir.
 if src is null no operation is done, if dir is null or there is no
 current file the cache is deleted.

 Function called when loading a new class library.

This function may be called after having filled some entries in a Tree
Using the information in the existing branch buffers, it will reassign
new branch buffer sizes to optimize time and memory.

The function computes the best values for branch buffer sizes such that
the total buffer sizes is less than maxMemory and nearby entries written
at the same time.
In case the branch compression factor for the data written so far is less
than compMin, the compression is disabled.

if option ="d" an analysis report is printed.

 Interface to the Principal Components Analysis class.

   Create an instance of TPrincipal
   Fill it with the selected variables
   if option "n" is specified, the TPrincipal object is filled with
                 normalized variables.
   If option "p" is specified, compute the principal components
   If option "p" and "d" print results of analysis
   If option "p" and "h" generate standard histograms
   If option "p" and "c" generate code of conversion functions
   return a pointer to the TPrincipal object. It is the user responsibility
   to delete this object.
   The option default value is "np"

   see TTree::Draw for explanation of the other parameters.

   The created object is  named "principal" and a reference to it
   is added to the list of specials Root objects.
   you can retrieve a pointer to the created object via:
      TPrincipal *principal =
        (TPrincipal*)gROOT->GetListOfSpecials()->FindObject("principal");

 Print a summary of the tree contents.

 If option contains "all" friend trees are also printed.
 If option contains "toponly" only the top level branches are printed.
 If option contains "clusters" information about the cluster of baskets is printed.

 Wildcarding can be used to print only a subset of the branches, e.g.,
 T.Print("Elec*") will print all branches with name starting with "Elec".

 print statistics about the TreeCache for this tree, like
   ******TreeCache statistics for file: cms2.root ******
   Reading 73921562 bytes in 716 transactions
   Average transaction = 103.242405 Kbytes
   Number of blocks in current cache: 202, total size : 6001193

 if option = "a" the list of blocks in the cache is printed

 Process this tree executing the TSelector code in the specified filename.
 The return value is -1 in case of error and TSelector::GetStatus() in
 in case of success.

 The code in filename is loaded (interpreted or compiled, see below),
 filename must contain a valid class implementation derived from TSelector,
 where TSelector has the following member functions:

    Begin():        called every time a loop on the tree starts,
                    a convenient place to create your histograms.
    SlaveBegin():   called after Begin(), when on PROOF called only on the
                    slave servers.
    Process():      called for each event, in this function you decide what
                    to read and fill your histograms.
    SlaveTerminate: called at the end of the loop on the tree, when on PROOF
                    called only on the slave servers.
    Terminate():    called at the end of the loop on the tree,
                    a convenient place to draw/fit your histograms.

 If filename is of the form file.C, the file will be interpreted.
 If filename is of the form file.C++, the file file.C will be compiled
 and dynamically loaded.
 If filename is of the form file.C+, the file file.C will be compiled
 and dynamically loaded. At next call, if file.C is older than file.o
 and file.so, the file.C is not compiled, only file.so is loaded.

  NOTE1
  It may be more interesting to invoke directly the other Process function
  accepting a TSelector* as argument.eg
     MySelector *selector = (MySelector*)TSelector::GetSelector(filename);
     selector->CallSomeFunction(..);
     mytree.Process(selector,..);

  NOTE2
  One should not call this function twice with the same selector file
  in the same script. If this is required, proceed as indicated in NOTE1,
  by getting a pointer to the corresponding TSelector,eg
    workaround 1

void stubs1() {
   TSelector *selector = TSelector::GetSelector("h1test.C");
   TFile *f1 = new TFile("stubs_nood_le1.root");
   TTree *h1 = (TTree*)f1->Get("h1");
   h1->Process(selector);
   TFile *f2 = new TFile("stubs_nood_le1_coarse.root");
   TTree *h2 = (TTree*)f2->Get("h1");
   h2->Process(selector);
}
  or use ACLIC to compile the selector
   workaround 2

void stubs2() {
   TFile *f1 = new TFile("stubs_nood_le1.root");
   TTree *h1 = (TTree*)f1->Get("h1");
   h1->Process("h1test.C+");
   TFile *f2 = new TFile("stubs_nood_le1_coarse.root");
   TTree *h2 = (TTree*)f2->Get("h1");
   h2->Process("h1test.C+");
}

 Process this tree executing the code in the specified selector.
 The return value is -1 in case of error and TSelector::GetStatus() in
 in case of success.

   The TSelector class has the following member functions:

    Begin():        called every time a loop on the tree starts,
                    a convenient place to create your histograms.
    SlaveBegin():   called after Begin(), when on PROOF called only on the
                    slave servers.
    Process():      called for each event, in this function you decide what
                    to read and fill your histograms.
    SlaveTerminate: called at the end of the loop on the tree, when on PROOF
                    called only on the slave servers.
    Terminate():    called at the end of the loop on the tree,
                    a convenient place to draw/fit your histograms.

  If the Tree (Chain) has an associated EventList, the loop is on the nentries
  of the EventList, starting at firstentry, otherwise the loop is on the
  specified Tree entries.

 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.

 Loop over entries and return a TSQLResult object containing entries following selection.

 Create or simply read branches from filename.

 if branchDescriptor = "" (default), it is assumed that the Tree descriptor
    is given in the first line of the file with a syntax like
     A/D:Table[2]/F:Ntracks/I:astring/C
  otherwise branchDescriptor must be specified with the above syntax.
  -If the type of the first variable is not specified, it is assumed to be "/F"
  -if the type of any other variable is not specified, the type of the previous
    variable is assumed. eg
      x:y:z      (all variables are assumed of type "F"
      x/D:y:z    (all variables are of type "D"
      x:y/D:z    (x is type "F", y and z of type "D"

  delimiter allows for the use of another delimiter besides whitespace.
    This provides support for direct import of common data file formats
    like csv.  If delimiter != ' ' and branchDescriptor == "", then the
    branch description is taken from the first line in the file, but
    delimiter is used for the branch names tokenization rather than ':'.
    Note however that if the values in the first line do not use the
    /[type] syntax, all variables are assumed to be of type "F".
    If the filename ends with extensions .csv or .CSV and a delimiter is
    not specified (besides ' '), the delimiter is automatically set to ','.

 Lines in the input file starting with "#" are ignored. Leading whitespace
   for each column data is skipped. Empty lines are skipped.

 A TBranch object is created for each variable in the expression.
 The total number of rows read from the file is returned.

 FILLING a TTree WITH MULTIPLE INPUT TEXT FILES

 To fill a TTree with multiple input text files, proceed as indicated above
 for the first input file and omit the second argument for subsequent calls
    T.ReadFile("file1.dat","branch descriptor");
    T.ReadFile("file2.dat");

 Determine which newline this file is using.
 Return '\r' for Windows '\r\n' as that already terminates.

 Create or simply read branches from an input stream.

 See reference information for TTree::ReadFile

 Make sure that obj (which is being deleted or will soon be) is no
 longer referenced by this TTree.

  Refresh contents of this tree and its branches from the current status on disk.

  One can call this function in case the tree file is being
  updated by another process.

 Remove a friend from the list of friends.

 Reset baskets, buffers and entries count in all branches and leaves.

 Resets the state of this TTree after a merge (keep the customization but
 forget the data).

 Tell all of our branches to set their addresses to zero.

 Note: If any of our branches own any objects, they are deleted.

 Tell all of our branches to drop their current objects and allocate new ones.

 Loop over tree entries and print entries passing selection.

 If varexp is 0 (or "") then print only first 8 columns.
 If varexp = "*" print all columns.
 Otherwise a columns selection can be made using "var1:var2:var3".
 See TTreePlayer::Scan for more information

 Set a tree variable alias.

  Set an alias for an expression/formula based on the tree 'variables'.

  The content of 'aliasName' can be used in TTreeFormula (i.e. TTree::Draw,
  TTree::Scan, TTreeViewer) and will be evaluated as the content of
  'aliasFormula'.
  If the content of 'aliasFormula' only contains symbol names, periods and
  array index specification (for example event.fTracks[3]), then
  the content of 'aliasName' can be used as the start of symbol.

  If the alias 'aliasName' already existed, it is replaced by the new
  value.

  When being used, the alias can be preceded by an eventual 'Friend Alias'
  (see TTree::GetFriendAlias)

  Return true if it was added properly.

  For example:
     tree->SetAlias("x1","(tdc1[1]-tdc1[0])/49");
     tree->SetAlias("y1","(tdc1[3]-tdc1[2])/47");
     tree->SetAlias("x2","(tdc2[1]-tdc2[0])/49");
     tree->SetAlias("y2","(tdc2[3]-tdc2[2])/47");
     tree->Draw("y2-y1:x2-x1");

     tree->SetAlias("theGoodTrack","event.fTracks[3]");
     tree->Draw("theGoodTrack.fPx"); // same as "event.fTracks[3].fPx"

 This function may be called at the start of a program to change
 the default value for fAutoFlush.

     CASE 1 : autof > 0

 autof is the number of consecutive entries after which TTree::Fill will
 flush all branch buffers to disk.

     CASE 2 : autof < 0

 When filling the Tree the branch buffers will be flushed to disk when
 more than autof bytes have been written to the file. At the first FlushBaskets
 TTree::Fill will replace fAutoFlush by the current value of fEntries.

 Calling this function with autof<0 is interesting when it is hard to estimate
 the size of one entry. This value is also independent of the Tree.

 The Tree is initialized with fAutoFlush=-30000000, ie that, by default,
 the first AutoFlush will be done when 30 MBytes of data are written to the file.

     CASE 3 : autof = 0

 The AutoFlush mechanism is disabled.

 Flushing the buffers at regular intervals optimize the location of
 consecutive entries on the disk by creating clusters of baskets.

 A cluster of baskets is a set of baskets that contains all
 the data for a (consecutive) set of entries and that is stored
 consecutively on the disk.   When reading all the branches, this
 is the minimum set of baskets that the TTreeCache will read.

This function may be called at the start of a program to change
the default value for fAutoSave(300000000, ie 300 MBytes).
When filling the Tree the branch buffers as well as the Tree header
will be flushed to disk when more than fAutoSave bytes have been written to the file.
In case of a program crash, it will be possible to recover the data in the Tree
up to the last AutoSave point.

 Set a branch's basket size.

 bname is the name of a branch.
 if bname="*", apply to all branches.
 if bname="xxx*", apply to all branches with name starting with xxx
 see TRegexp for wildcarding options
 buffsize = branc basket size

 Change branch address, dealing with clone trees properly.
 See TTree::CheckBranchAddressType for the semantic of the return value.

 Note: See the comments in TBranchElement::SetAddress() for the
       meaning of the addr parameter and the object ownership policy.

 Verify the validity of the type of addr before calling SetBranchAddress.
 See TTree::CheckBranchAddressType for the semantic of the return value.

 Note: See the comments in TBranchElement::SetAddress() for the
       meaning of the addr parameter and the object ownership policy.

 Verify the validity of the type of addr before calling SetBranchAddress.
 See TTree::CheckBranchAddressType for the semantic of the return value.

 Note: See the comments in TBranchElement::SetAddress() for the
       meaning of the addr parameter and the object ownership policy.

 Change branch address, dealing with clone trees properly.
 See TTree::CheckBranchAddressType for the semantic of the return value.

 Note: See the comments in TBranchElement::SetAddress() for the
       meaning of the addr parameter and the object ownership policy.

 Set branch status to Process or DoNotProcess.

  When reading a Tree, by default, all branches are read.
  One can speed up considerably the analysis phase by activating
  only the branches that hold variables involved in a query.

     bname is the name of a branch.
     if bname="*", apply to all branches.
     if bname="xxx*", apply to all branches with name starting with xxx
     see TRegexp for wildcarding options
      status = 1  branch will be processed
             = 0  branch will not be processed
    Example:
  Assume a tree T with sub-branches a,b,c,d,e,f,g,etc..
  when doing T.GetEntry(i) all branches are read for entry i.
  to read only the branches c and e, one can do
    T.SetBranchStatus("*",0); //disable all branches
    T.SetBranchStatus("c",1);
    T.setBranchStatus("e",1);
    T.GetEntry(i);

  bname is interpreted as a wildcarded TRegexp (see TRegexp::MakeWildcard).
  Thus, "a*b" or "a.*b" matches branches starting with "a" and ending with
  "b", but not any other branch with an "a" followed at some point by a
  "b". For this second behavior, use "*a*b*". Note that TRegExp does not
  support '|', and so you cannot select, e.g. track and shower branches
  with "track|shower".

  WARNING! WARNING! WARNING!
  SetBranchStatus is matching the branch based on match of the branch
  'name' and not on the branch hierarchy! In order to be able to
  selectively enable a top level object that is 'split' you need to make
  sure the name of the top level branch is prefixed to the sub-branches'
  name (by adding a dot ('.') at the end of the Branch creation and use the
  corresponding bname.

  I.e If your Tree has been created in split mode with a parent branch "parent."
  (note the trailing dot).
     T.SetBranchStatus("parent",1);
  will not activate the sub-branches of "parent". You should do:
     T.SetBranchStatus("parent*",1);

  Without the trailing dot in the branch creation you have no choice but to
  call SetBranchStatus explicitly for each of the sub branches.


  An alternative to this function is to read directly and only
  the interesting branches. Example:
    TBranch *brc = T.GetBranch("c");
    TBranch *bre = T.GetBranch("e");
    brc->GetEntry(i);
    bre->GetEntry(i);

  If found is not 0, the number of branch(es) found matching the regular
  expression is returned in *found AND the error message 'unknown branch'
  is suppressed.

 Set the current branch style.  (static function)

 style = 0 old Branch
 style = 1 new Bronch

 Set maximum size of the file cache .
 if cachesize = 0 the existing cache (if any) is deleted.
 if cachesize = -1 (default) it is set to the AutoFlush value when writing
    the Tree (default is 30 MBytes).

 Set the size of the file cache and create it if needed.

 If autocache is true:
 this will be an automatically create cache, possibly replacing an
 existing autocreated cache with a larger one. The size is calculated,
 cacheSize is unused.

 If autocache is false:
 cacheSize is used to size the cache. This cache should never be
 automatically adjusted.

interface to TTreeCache to set the cache entry range

interface to TTreeCache to set the number of entries for the learning phase

 Enable/Disable circularity for this tree.

 if maxEntries > 0 a maximum of maxEntries is kept in one buffer/basket
 per branch in memory.
   Note that when this function is called (maxEntries>0) the Tree
   must be empty or having only one basket per branch.
 if maxEntries <= 0 the tree circularity is disabled.

 NOTE 1:
  Circular Trees are interesting in online real time environments
  to store the results of the last maxEntries events.
 NOTE 2:
  Calling SetCircular with maxEntries <= 0 is necessary before
  merging circular Trees that have been saved on files.
 NOTE 3:
  SetCircular with maxEntries <= 0 is automatically called
  by TChain::Merge
 NOTE 4:
  A circular Tree can still be saved in a file. When read back,
  it is still a circular Tree and can be filled again.

 Set the debug level and the debug range.

 For entries in the debug range, the functions TBranchElement::Fill
 and TBranchElement::GetEntry will print the number of bytes filled
 or read for each branch.

 Update the default value for the branch's fEntryOffsetLen.
 If updateExisting is true, also update all the existing branches.
 If newdefault is less than 10, the new default value will be 10.

 Change the tree's directory.

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

 Change number of entries in the tree.

 If n >= 0, set number of entries in the tree = n.

 If n < 0, set number of entries in the tree to match the
 number of entries in each branch. (default for n is -1)

 This function should be called only when one fills each branch
 independently via TBranch::Fill without calling TTree::Fill.
 Calling TTree::SetEntries() make sense only if the number of entries
 in each branch is identical, a warning is issued otherwise.
 The function returns the number of entries.

Set an EntryList

This function transfroms the given TEventList into a TEntryList
The new TEntryList is owned by the TTree and gets deleted when the tree
is deleted. This TEntryList can be returned by GetEntryList() function.

 Set number of entries to estimate variable limits.
 If n is -1, the estimate is set to be the current maximum
 for the tree (i.e. GetEntries() + 1)
 If n is less than -1, the behavior is undefined.

 Set fFileNumber to number.
 fFileNumber is used by TTree::Fill to set the file name
 for a new file to be created when the current file exceeds fgTreeMaxSize.
    (see TTree::ChangeFile)
 if fFileNumber=10, the new file name will have a suffix "_11",
 ie, fFileNumber is incremented before setting the file name

 Set all the branches in this TTree to be in decomposed object mode
 (also known as MakeClass mode).

 Set the maximum size in bytes of a Tree file (static function).
 The default size is 100000000000LL, ie 100 Gigabytes.

 In TTree::Fill, when the file has a size > fgMaxTreeSize,
 the function closes the current file and starts writing into
 a new file with a name of the style "file_1.root" if the original
 requested file name was "file.root".

 Change the name of this tree.

 Change the name and title of this tree.

 Enable or disable parallel unzipping of Tree buffers.

 The current TreeIndex is replaced by the new index.
 Note that this function does not delete the previous index.
 This gives the possibility to play with more than one index, e.g.,
 TVirtualIndex* oldIndex = tree.GetTreeIndex();
 tree.SetTreeIndex(newIndex);
 tree.Draw();
 tree.SetTreeIndex(oldIndex);
 tree.Draw(); etc

 Set tree weight.

 The weight is used by TTree::Draw to automatically weight each
 selected entry in the resulting histogram.

 For example the equivalent of:

      T.Draw("x", "w")

 is:

      T.SetWeight(w);
      T.Draw("x");

 This function is redefined by TChain::SetWeight. In case of a
 TChain, an option "global" may be specified to set the same weight
 for all trees in the TChain instead of the default behaviour
 using the weights of each tree in the chain (see TChain::SetWeight).

 Print values of all active leaves for entry.

 if entry==-1, print current entry (default)
 if a leaf is an array, a maximum of lenmax elements is printed.

 Start the TTreeViewer on this tree.

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

 stop the cache learning phase

 Stream a class object.

 Unbinned fit of one or more variable(s) from a tree.

  funcname is a TF1 function.

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

   Fit the variable varexp using the function funcname using the
   selection cuts given by selection.

   The list of fit options is given in parameter option.
      option = "Q" Quiet mode (minimum printing)
             = "V" Verbose mode (default is between Q and V)
             = "E" Perform better Errors estimation using Minos technique
             = "M" More. Improve fit results

   You can specify boundary limits for some or all parameters via
        func->SetParLimits(p_number, parmin, parmax);
   if parmin>=parmax, the parameter is fixed
   Note that you are not forced to fix the limits for all parameters.
   For example, if you fit a function with 6 parameters, you can do:
     func->SetParameters(0,3.1,1.e-6,0.1,-8,100);
     func->SetParLimits(4,-10,-4);
     func->SetParLimits(5, 1,1);
   With this setup, parameters 0->3 can vary freely
   Parameter 4 has boundaries [-10,-4] with initial value -8
   Parameter 5 is fixed to 100.

   For the fit to be meaningful, the function must be self-normalized.

   i.e. It must have the same integral regardless of the parameter
   settings.  Otherwise the fit will effectively just maximize the
   area.

   It is mandatory to have a normalization variable
   which is fixed for the fit.  e.g.

     TF1* f1 = new TF1("f1", "gaus(0)/sqrt(2*3.14159)/[2]", 0, 5);
     f1->SetParameters(1, 3.1, 0.01);
     f1->SetParLimits(0, 1, 1); // fix the normalization parameter to 1
     data->UnbinnedFit("f1", "jpsimass", "jpsipt>3.0");


   1, 2 and 3 Dimensional fits are supported.
   See also TTree::Fit

    Return status

   The function return the status of the fit in the following form
     fitResult = migradResult + 10*minosResult + 100*hesseResult + 1000*improveResult
   The fitResult is 0 is the fit is OK.
   The fitResult is negative in case of an error not connected with the fit.
   The number of entries used in the fit can be obtained via
     mytree.GetSelectedRows();
   If the number of selected entries is null the function returns -1

 Replace current attributes by current style.

 Write this object to the current directory. For more see TObject::Write
 Write calls TTree::FlushBaskets before writing the tree.

 Write this object to the current directory. For more see TObject::Write
 If option & kFlushBasket, call FlushBasket before writing the tree.

 GetMakeClass is left non-virtual for efficiency reason.
 Making it virtual affects the performance of the I/O

 See TSelectorDraw::GetVar

 See TSelectorDraw::GetVar

 See TSelectorDraw::GetVar

 See TSelectorDraw::GetVar

 See TSelectorDraw::GetVar

 See TSelectorDraw::GetVal

 See TSelectorDraw::GetVal

 See TSelectorDraw::GetVal

 See TSelectorDraw::GetVal

 See TSelectorDraw::GetVal