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These lines create and fill an unbinned histogram named nTracks with the return value of tracks.size()
Teminology
AIDA provides two different kinds of histograms: binned and unbinned.
Binned histograms are called IHistogram1D, IHistogram2D, and IHistogram3D for one, two and three-dimensional histograms.
Similarly, unbinned histograms are called ICloud1D, ICloud2D, and ICloud3D
Getting started
Viewing and Loading Plots
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While it is convenient to be able to manipulate your data with the mouse, in many cases you will want to apply the same modifications to a set of similar data, or perform more complicated modifications that are quite possible to do with AIDA, but not (yet) implemented in JAS3. This is where a script comes in handy
Advanced Manipulations of Histograms
Adding and subtracting histograms
Fitting
Using predefined functions
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