class RooDataHist: public RooTreeData, public RooDirItem

 Default constructor

 Constructor of an empty data hist from a RooArgSet defining the dimensions
 of the data space. The range and number of bins in each dimensions are taken
 from getMin()getMax(),getBins() of each RooAbsArg representing that
 dimension.

 For real dimensions, the fit range and number of bins can be set independently
 of the plot range and number of bins, but it is advisable to keep the
 ratio of the plot bin width and the fit bin width an integer value.
 For category dimensions, the fit ranges always comprises all defined states
 and each state is always has its individual bin

 To effective achive binning of real dimensions with variable bins sizes,
 construct a RooThresholdCategory of the real dimension to be binned variably.
 Set the thresholds at the desired bin boundaries, and construct the
 data hist as function of the threshold category instead of the real variable.

 Constructor of a data hist from an existing data collection (binned or unbinned)
 The RooArgSet 'vars' defines the dimensions of the histogram.
 The range and number of bins in each dimensions are taken
 from getMin()getMax(),getBins() of each RooAbsArg representing that
 dimension.

 For real dimensions, the fit range and number of bins can be set independently
 of the plot range and number of bins, but it is advisable to keep the
 ratio of the plot bin width and the fit bin width an integer value.
 For category dimensions, the fit ranges always comprises all defined states
 and each state is always has its individual bin

 To effective achive binning of real dimensions with variable bins sizes,
 construct a RooThresholdCategory of the real dimension to be binned variably.
 Set the thresholds at the desired bin boundaries, and construct the
 data hist as function of the threshold category instead of the real variable.

 If the constructed data hist has less dimensions that in source data collection,
 all missing dimensions will be projected.

 Constructor of a data hist from an TH1,TH2 or TH3
 The RooArgSet 'vars' defines the dimensions of the histogram. The ranges
 and number of bins are taken from the input histogram, and the corresponding
 values are set accordingly on the arguments in 'vars'

 Initialization procedure: allocate weights array, calculate
 multipliers needed for N-space to 1-dim array jump table,
 and fill the internal tree with all bin center coordinates

 Copy constructor

 Constructor of a data hist from (part of) an existing data hist. The dimensions
 of the data set are defined by the 'vars' RooArgSet, which can be identical
 to 'dset' dimensions, or a subset thereof. Reduced dimensions will be projected
 in the output data hist. The optional 'cutVar' formula variable can used to
 select the subset of bins to be copied.

 For most uses the RooAbsData::reduce() wrapper function, which uses this constructor,
 is the most convenient way to create a subset of an existing data

 Implementation of RooAbsData virtual method that drives the RooAbsData::reduce() methods

 Destructor

 Calculate the index for the weights array corresponding to
 to the bin enclosing the current coordinates of the internal argset

 Debug stuff, should go...

 Return the weight at given coordinates with optional
 interpolation. If intOrder is zero, the weight
 for the bin enclosing the coordinates
 contained in 'bin' is returned. For higher values,
 the result is interpolated in the real dimensions
 of the dataset

 Return error on current weight

 Perform boundary safe 'intOrder'-th interpolation of weights in dimension 'dim'
 at current value 'xval'

 Increment the weight of the bin enclosing the coordinates
 given by 'row' by the specified amount

 Increment the weight of the bin enclosing the coordinates
 given by 'row' by the specified amount

 Increment the weight of the bin enclosing the coordinates
 given by 'row' by the specified amount

 Add all data points contained in 'dset' to this data set with given weight.
 Optional cut string expression selects the data points to be added and can
 reference any variable contained in this data set

 Add all data points contained in 'dset' to this data set with given weight.
 Optional RooFormulaVar pointer selects the data points to be added.

 Return the sum of the weights of all hist bins.

 If correctForBinSize is specified, the sum of weights
 is multiplied by the N-dimensional bin volume,
 making the return value the integral over the function
 represented by this histogram

 Return the sum of the weights of a multi-dimensional slice of the histogram
 by summing only over the dimensions specified in sumSet.

 The coordinates of all other dimensions are fixed to those given in sliceSet

 If correctForBinSize is specified, the sum of weights
 is multiplied by the M-dimensional bin volume, (M = N(sumSet)),
 making the return value the integral over the function
 represented by this histogram

 Allocate cache if not yet existing

 Return the number of bins (useWeights=false) or
 the sum of the weights of all bins (useWeight=true)

 Reset all bin weights to zero

 Return an argset with the bin center coordinates for
 bin sequential number 'masterIdx'. For iterative use.

 Add one ore more rows of data