I am new to root. I have several basic questions. 1. I am having difficulty understanding how root handles events in which there may be several instances of a detector - for instance 6 detectors each with the same 4 parameters. There are so many kinds of lengths defined for a branch: there is fLen, GetLen, GetLenStatic, GetLeafCount, GetLeafCounter, GetMaximum. What role does each one play. 2. There appears to be a great deal of care in how the names of leaves are used so that they may be used in selection expressions, formulas, etc. 2a. In a TNamed, what is the difference between a name and a title ? When I was reading the code for (I think) Leaf::GetValue() I found it was using information from the title rather than the name to match names appearing in selection expressions. Why ? 2b. How does one refer to the Nth element of an array of detectors, assuming they are all in the same branch. I suppose this would involve the use of a branch containing a TObjArray. 2c. Suppose an element of the array (branch B) has four 16 bit shorts named p, q, r, and s. How does one refer to branch B, detector 2, part "s" in a selection expression ? 3. There appears to be support for the population of a histogram and event selection using cuts built into TTree. It appears to handle exactly one such histogram. If one wants to populate many histograms in a single pass through the event data does one call use Fill, Cut, CutG, etc. by making explicit calls ? 4. How do users handle bit patterns ? Suppose one has a 16 bit word in which each bit indicates a condition and one wants to give them symbolic names for use in selection expressions. Is there a recommended way to do this, or does one simply use the bitwise "|" and "&" operators in combination with bit masks. Tom Moog
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