Hi Benoit, Fitting in ROOT is via the TMinuit class. With TMinuit, one can perform fits on N dimensional distributions with P parameters. In case of 1-D, 2-D and 3-D histograms, Profile histograms and TGraph Fit functions are provided for these classes. In the tutorials section, we show several examples of fits on 1-D histograms. In the test program in $ROOTSYS/test/stress.cxx, you can see an example (stress4) of a fit on a 2-D histogram. In this example, the fit function f2form is given as a simple expression made of standard basic functions. In real life problems, one better uses a standard C++ function of a form always the same for all dimensions and problems: Double_t myFunction(Double_t *x, Double_t *params) Here is a variant of stress4 using the second form Rene Brun // file fit2.C #include "TF2.h" #include "TH2.h" // This tutorial illustrates : // - how to create a 2-d function // - fill a 2-d histogram randomly from this function // - fit the histogram // - display the fitted function on top of the histogram (scatter-plot) // // This example can be executed via the interpreter or/and the compiler // root > .x fit2.C // root > .x fit2.C++ Double_t g2(Double_t *x, Double_t *par) { Double_t r1 = Double_t((x[0]-par[1])/par[2]); Double_t r2 = Double_t((x[1]-par[3])/par[4]); return par[0]*TMath::Exp(-0.5*(r1*r1+r2*r2)); } Double_t fun2(Double_t *x, Double_t *par) { Double_t *p1 = &par[0]; Double_t *p2 = &par[5]; Double_t *p3 = &par[10]; Double_t result = g2(x,p1) + g2(x,p2) + g2(x,p3); return result; } void fit2() { const Int_t npar = 15; Double_t f2params[npar] = {100,-3,3,-3,3,160,0,0.8,0,0.9,40,4,0.7,4,0.7}; TF2 *f2 = new TF2("f2",fun2,-10,10,-10,10, npar); f2->SetParameters(f2params); //Create an histogram and fill it randomly with f2 TH2F *h2 = new TH2F("h2","from f2",40,-10,10,40,-10,10); Int_t nentries = 100000; h2->FillRandom("f2",nentries); //Fit h2 with original function f2 Float_t ratio = 4*nentries/100000; f2params[ 0] *= ratio; f2params[ 5] *= ratio; f2params[10] *= ratio; f2->SetParameters(f2params); h2->Fit("f2"); f2->Draw("cont1 same"); } FORESTIER Benoit wrote: > > hi, > is it possible, using ROOT, to perform a 2D fit? > > Benoit Forestier
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