Hi, ROOTers: I have a question on using TMinuit. I read the tutorial "Ifit.C", but it did not answer my question. I am using ROOT 3.10.00 self-compiled on Mandrake 9.1. In "Ifit.C", the data points "Float_t z[5],x[5],y[5],errorz[5];" are global variables. This is understandable, since "void fcn(Int_t &npar, Double_t *gin, Double_t &f, Double_t *par, Int_t iflag)" has not idea what data points to use beforehand. However, this is ugly, not particularly safe. Now suppose I want to make a custom fitter for my own class. Data points will come from the members of the class (actually I will reload the data members every event, use the fitter, and write fit result to a tree). Can I call "TMinuit::SetFCN(...)" on a memeber function "void fcn(Int_t &npar, Double_t *gin, Double_t &f, Double_t *par, Int_t iflag)" (so it knows the member data, without the need to make the data global)? Is this possible? Or there is a better solution? Thanks in advance! Yiqun Wang
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