Hi Vladimir,
In your fitFunction, replace the line:
return &par[0]*TMath::Landau(xx,.02,.005);
by
return par[0]*TMath::Landau(xx,.02,.005);
Rene Brun
On Sun, 17 Mar 2002, Vladimir Morozov wrote:
> I'm having trouble fitting a histogram to Landau distribution in a
> limited variable range.
> Here's a macro, which will build a histogram, fill it and try to fit it
> to Landau. The fit always fails (cannot find an appropriate value for
> fit parameters), and I don't know what's wrong. I've tried helping the
> fitter by providing a reasonable starting point for the fit, but it
> still doesn't work. Any idea what I might be doing wrong? I'm running
> Root4STAR 3.02/07
>
> Thanx,
> Vladimir.
>
> _______________________________________-
>
> #include <TMath.h>
>
> Double_t fitFunction(Double_t *x, Double_t *par) {
> Double_t xx = x[0];
> return &par[0]*TMath::Landau(xx,.02,.005);
> }
>
> void macro() {
>
> TH1 *histo = new TH1F("histo","pPt",19,-0.002,0.19);
> histo->SetEntries(174);
> histo->SetDirectory(0);
> histo->SetBinContent(1,12);
> histo->SetBinContent(2,22);
> histo->SetBinContent(3,18);
> histo->SetBinContent(4,10);
> histo->SetBinContent(5,8);
> histo->SetBinContent(6,8);
> histo->SetBinContent(7,3);
> histo->SetBinContent(8,3);
> histo->SetBinContent(9,2);
> histo->SetBinContent(10,3);
> histo->SetBinContent(11,1);
> histo->SetBinContent(12,1);
> histo->SetBinContent(13,1);
> histo->SetBinContent(14,1);
> histo->SetBinContent(15,7);
> histo->SetBinContent(16,3);
> histo->SetBinContent(17,8);
> histo->SetBinContent(19,4);
>
> histo->SetMarkerStyle(20);
> histo->Draw("");
>
> TF1 *fun = new TF1("fun",fitFunction,0.03,.12,1);
> fun->SetParameter(0,140.0);
> histo->Fit("fun","R");
> }
>
>
>
>
>
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