# How to fit in a sub-range of an histogram

    {
    // To see the output of this macro, click  here
    //      Example showing how to fit in a sub-range of an histogram
    //  An histogram is created and filled with the bin contents and errors
    //  defined in the table below.
    //  3 gaussians are fitted in sub-ranges of this histogram.
    //  A new function (a sum of 3 gaussians) is fitted on another subrange
    //  Note that when fitting simple functions, such as gaussians, the initial
    //  values of parameters are automatically computed by ROOT.
    //  In the more complicated case of the sum of 3 gaussians, the initial values
    //  of parameters must be given. In this particular case, the initial values
    //  are taken from the result of the individual fits.

       gROOT->Reset();
       const Int_t np = 49;
       Float_t x[np] = {1.913521, 1.953769, 2.347435, 2.883654, 3.493567,
                        4.047560, 4.337210, 4.364347, 4.563004, 5.054247,
                        5.194183, 5.380521, 5.303213, 5.384578, 5.563983,
                        5.728500, 5.685752, 5.080029, 4.251809, 3.372246,
                        2.207432, 1.227541, 0.8597788,0.8220503,0.8046592,
                        0.7684097,0.7469761,0.8019787,0.8362375,0.8744895,
                        0.9143721,0.9462768,0.9285364,0.8954604,0.8410891,
                        0.7853871,0.7100883,0.6938808,0.7363682,0.7032954,
                        0.6029015,0.5600163,0.7477068,1.188785, 1.938228,
                        2.602717, 3.472962, 4.465014, 5.177035};

       h = new TH1F("g1","Example of several fits in subranges",np,85,134);
       h->SetMaximum(7);

       for (int i=0;i<np;i++) {
          h->SetBinContent(i+1,x[i]);
       }

       Double_t par[9];
       g1    = new TF1("g1","gaus",85,95);
       g2    = new TF1("g2","gaus",98,108);
       g3    = new TF1("g3","gaus",110,121);
       total = new TF1("total","gaus(0)+gaus(3)+gaus(6)",85,125);
       total->SetLineColor(2);
       h->Fit("g1","R");
       h->Fit("g2","R+");
       h->Fit("g3","R+");
       g1->GetParameters(&par[0]);
       g2->GetParameters(&par[3]);
       g3->GetParameters(&par[6]);
       total->SetParameters(par);
       h->Fit("total","R0+");
       h->Draw();
    }