Hi Martin, You have a different binning in option1 and option2. Check limits and bin width. When using option1, Root computes automatically the profile limits and optimizes the limits around the min/max of the distribution. So, no surprise if you get slightly different ditributions. Rene Brun On Sat, 13 Jul 2002, Martin Turner wrote: > Hi, I noticed a perculiarity with TProfile. > > my_tree->Draw("var1:var2",cuts,"prof"); //option1 > gives a slightly different plot to: > > my_tree->Draw("var1:var2>>myprof,cuts); //option2 > > Now, the number of points, mean and rms of both plots are the same, so the > same data has gone into both. I set the number of bins in myprof to 100 > which I believe is the default number of bins when using the > "prof" option. Nothing is cut out on the TProfile initialiser, so the > number of non zero points are the same for both. The only difference is > that a small percentage of the points are in different places. > > I looked into a very zoomed in region of both plots and it appeared that > the bin boundaries are different for option1 and 2. Fits to option2 give > better chi squareds than option1, like a 7 or 8% effect, but I haven't > looked at enough examples to conclude anything about chi squareds. > I would like to understand what exactly is going on. Has anyone else > noticed this? > > Martin >
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