Hi Justin, Create your own functions to laboriously get the BinContent and BinError of each histo and manipulate them. Put them one by one into a new histogram. It is the best way to perform histogram mathematics. I personally don't trust ROOT (and didn't trust PAW) to handle my errors right ever. I have a small library of functions to add, subtract, multiply, divide, c=(a-b)/b, and on and on and on. In some cases I pay attention only to the errors of one histogram, in others I watch both histograms. I include below an example from my library. - John // a kind of scaled subtraction a=(b-c+d)/d, with errors preserved // The extra +d puts the result back near 1.0 instead of near 0.0 TH1F * hbd::sshist(TH1F *a, TH1F *b, TH1F *c, TH1F *d){ Double_t bc,cc,be,dc; for (Int_t i=1; i< b->GetNbinsX(); i++){ bc=b->GetBinContent(i); cc=c->GetBinContent(i); dc=d->GetBinContent(i); be=b->GetBinError(i); if (dc && cc && bc) a->SetBinContent(i,(bc-cc+dc)/dc); a->SetBinError(i,0.0); } return a; } Justin Findlay wrote: >Hi, > >I have a function composed of some constants and some random variables >(ntuple columns) like this: > >f(w, x, y, z) = 20.0 *(x - y)-(w + 1000.0 /(z - y)) > >How can I use this function as an axis of an histogram with the combined >errors of each random variable correctly computed and displayed in the >histogram? Thanks, > > >Justin > > >
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