in my code (complex C++ program) I use in several places the TTree::Draw() calls. The strange thing is that sometimes the resulting histograms are empty, but the number of histogram entries is not (and I am absolutely sure about the hisogram range). The problem is difficult to reproduce (I failed to create a simple program which illustrates it), but if the problem is seen on some data and with some TTree cuts, it is reproducible. Exactly the same executable file may produce normal histograms on a different data (or with different TTree cuts).
I added a TTree::Scan() call (for the same expression which I used in TTree::Draw()) and it gives me non-empty values.
Did anyone observe such a behavior? What could be the reason?
In the broken cases, all the data for in the overflow bin.
(you can verify this by call myhist->Print(“all”) for example).
You will also notice that this seem to be the correct result.
For[code]main ERROR plot_SB: elist=702 name=“asym_vc_Ds_VC2P_fDPp” var=“spinZ[cell]beam_poldil[cell]*depol” weight="" entries=702 mean=0 RMS=0
main ERROR plot_SB: elist was: “(abs(lv[0].Mag()-1.8645)<0.05)&&((((1)&&(Ds_id&&Ds_zD&&Ds_cos&&common&&cut_dM))&&((1)&&(Ds_id&&Ds_zD&&Ds_cos&&common&&cut_dM)))&&(vc2&&spinP))”
Row * spinZ[cel *
93 * 3.0434739 *
117 * 9.7618281 *
************************[/code]
The range your histo is -.5 to .5