Hi Alexey,
What you do below is correct. If an histogram has multiple associated
fitted functions, you get a pointer to one function via
hist->GetFunction(functionName);
You have likely a different problem in your example.
You use the results of the first fit to set the range of the second fit.
By default, the first function is fitted using the histogram range.
The range of the second function is likely larger than the original
histogram. In this case, the parameters of the first and second fit will
be identical.
In your example you are fitting with a gaussian an histogram with a few
entries only. You should request the "log likelihood method" instead of
the
default "chisquare" method using the fitting option "l".
hist->Fit("gaus","l");
hist->Fit("limited","lR0+");
Rene Brun
Alexey Toptygin wrote:
>
> Hi,
> If you create a histogram with 2 or more functions, how do you get the fit
> statistics to correspond to a particular function?
> For Example, I do:
>
> TFile file("Science.root");
> gStyle->SetOptStat(1110);
> gStyle->SetOptFit(73);
> TCanvas *can;
> TH1F *hist;
> TF1 *fn,*lim;
> Double_t parm[3];
> Float_t width = 1.5;
>
> can = new TCanvas("canvas","Canvas",700,500);
> bgoir.Draw("val01","val01>10&&val01<99&&lay==0&&cry==15");
> hist = (TH1F*)can->GetPrimitive("htemp");
> hist->Fit("gaus");
> fn = hist->GetFunction("gaus");
> fn->GetParameters(parm);
> lim = new TF1("limited","gaus",parm[1]-width*parm[2],parm[1]+width*parm[2]);
> hist->Fit("limited","R0+");
>
> I get the stats for gaus, and I want to see the fit parameters for
> limited, not gaus?
> Thanks
> Alexey
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