Ratiofit_total = new TF1('ratiofit_total','ratiofit_lo+ratiofit_mid+ratiofit_hi', Ratio->GetBinLowEdge(ratio->GetNbinsX()+1)) Ratio->GetBinLowEdge(ratio->FindBin(200.)), TF1* ratiofit_hi = new TF1('ratiofit_hi','pol0', Ratio->GetBinLowEdge(ratio->FindBin(200.))) Ratio->GetBinLowEdge(ratio->FindBin(45.)), TF1* ratiofit_mid = new TF1('ratiofit_mid','pol3',

Ratio->GetBinLowEdge(ratio->FindBin(45.))) I thought the way around this would be to define another function which was the combination of all three following $ROOTSYS/tutorials/fit/multifit.C but this fit goes completely crazy (black curve in attachment) despite the individual ones being вЂњreasonableвЂќ so obviously something went wrong, but I canвЂ™t figure out what the problem is: TF1* ratiofit_lo = new TF1('ratiofit_lo','pol3',

I tried using three separate TF1вЂ™s defined over three separate intervals to piece-wise define the various parts of the TH1F, but this naturally has discontinuities at the boundaries. I am trying to fit a combination of TF1вЂ™s to a ratio represented by a TH1F to make a piecewise fit parameterising this ratio for later use (an example of the ratio and fits in attachment).

Piecewise function definition