#include <TH1.h>
#include <TF1.h>
#include <TROOT.h>

std::vector<TF1*> vfunc;
const int N = 4;
TH1F *h[N];

bool reject;
double fline(double *x, double *par)
{
    if (reject && x[0] > 2.5 && x[0] < 3.5) {
      TF1::RejectPoint();
      return 0;
   }
   return par[0] + par[1]*x[0];
}

void fitExclude() {
   TF1 *f1 = new TF1("f1","[0] +[1]*x +gaus(2)",0,5);
   f1->SetParameters(6,-1,5,3,0.2);

   vfunc.clear();

   for (int i = 0; i < N; ++i) {
     reject = true;
     if (i%2) reject = false;
     
     h[i] = new TH1F(Form("h%d",i),"background + signal",100,0,5);
     h[i]->FillRandom("f1",2000+i*100);

     TF1 *fl = new TF1("fl",fline,0,5,2);
     fl->SetParameters(2,-1);
     h[i]->Fit(fl,"QN");

     std::cout << Form("Fit_%d,  f(3) = %.4f",i,fl->Eval(3)) << std::endl;
     vfunc.emplace_back(fl);
   }
 }

void drawFit() {
  fitExclude();

  TCanvas *c = new TCanvas("c");
  c->Divide(2,2);
  for (int i = 0; i < N; ++i) {
    c->cd(i+1);
    h[i]->DrawCopy();
    vfunc[i]->DrawF1(0,5,"SAME");

    std::cout << Form("Draw_%d, f(3) = %.4f",i,vfunc[i]->Eval(3)) << std::endl;
  }
}