Hello Rooters, as I know the chi-square method, used to estimate parameters, goes like this: chisquare=sum_{i=1}^N (x_i - y_i)^2/e_i with x_i being the value from a spectrum and y_i being the theoretical function depending on one or more parameters. To get the best-fitting values for the parameters this function must be minimized. Suppose to fit a constant y with fit-option 'w' (setting all errors to 1). Then the chisquare-value should be calculated like this: chisquare=sum_{i=1}^N (x_i - y)^2 It is simple to calculate y for which this value is minimal: y=( sum_{i=1}^n x_i ) /n so y is simple the mean value of the data in the spectrum. I checked this with the following program: TH1F* h1=new TH1F("h1","test",10,1,10); h1->SetBinContent(3,1); h1->SetBinContent(7,2); h1->Fit("pol0","W"); but what I get is a best-value of 1.5 instead of 0.3! It seems that ROOT ignores every channel with zero-content. Is ROOT ignoring channels with zero-contente and why? What can I do that ROOT gives the correct value? Cheers Alexander Dietz
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