//file fit3.C
#include "TRandom3.h"
#include "Riostream.h"
#include <iostream>
#include "TH3.h"
#include "TF3.h"
#include "TMath.h"

double myfunc3(double *x, double *par) {
   double xx = (x[0] - par[1])/par[2];
   double yy = (x[1] - par[3])/par[4];
   double zz = (x[2] - par[5])/par[6];
   double rx = TMath::Exp(-xx*xx);
   double ry = TMath::Exp(-yy*yy);
   double rz = TMath::Exp(-zz*zz);
   double result = par[0]*rx*ry*rz;
   return result;
}
void fit3() {

   const unsigned nPts1 = 15;
   ifstream in1;
   in1.open("data_test.txt");

   Float_t x1,y1,z1;

   TCanvas *c1 = new TCanvas("c1"," ",0,0,700,350);

   TH3F *h1 = new TH3F("h1","h1",100,1000,3000,100,0.5,1.0,100,0.0,1.0);

      for (unsigned i = 0; i < nPts1; ++i) {
      in1 >> x1 >> y1 >> z1;
      if (!in1.good()) break;
      h1->Fill(x1,y1,z1);
      }

   in1.close();

   c1->cd();
   TF3 *func3 = new TF3("func3",myfunc3,1000,3000,0.5,1.0,0.0,1.0,7);
   func3->SetParameters(h1->GetMaximum(),0,0.5,0,0.5,0,0.5);
   h1->Fit(func3,"r+","E");

   h1->Draw("col");
   func3->Draw("same");
   func3->SetLineColor(kOrange+8);
   func3->SetLineStyle(1);
   func3->SetLineWidth(2);
   h1->SetMarkerStyle(20);
   h1->SetMarkerSize(1.0);
   h1->SetMarkerColor(kBlue);

   c1->Update();
}