#include "TFile.h"
#include "TMultiGraph.h"
#include "TGraph.h"
#include "TObject.h"
#include "TRandom.h"
#include <string>
#include <sstream>

using namespace std;


TGraph* generate_graph()
{
   double rnd, x, y, z;
   double e = 0.3;
   int nd = 500;

   TRandom r;
   TF1  *f1 = new TF1("f2","1000*(sin(x)/x)+200",-6,6);
   TGraph *dte = new TGraph(nd);

   // Fill the 2D graph
   double zmax = 0;
   for (int i=0; i<nd; i++) {
      x = f1->GetRandom();      
      rnd = r.Uniform(-e,e); // Generate a random number in [-e,e]
      z = f1->Eval(x)*(1+rnd);
      if (z>zmax) zmax = z;
      dte->SetPoint(i,x,z);
   }
   return dte;
}


void add_multi_graph(int i){

  TFile file("graphs.root","UPDATE");
  TMultiGraph *multi_gr; 
  if(i != 0) multi_gr = (TMultiGraph*)(file.Get("graphs"));  
  multi_gr->Add((TGraph*)(generate_graph()));
  multi_gr->Write("graphs", TObject::kOverwrite);
  
  file.Close();
  
}


int main(){
  int n = 3;
  
  TFile file("graphs.root","UPDATE");
  TMultiGraph *multi_gr[n]; 
  
  for(int i =0; i<n;i++){
     add_multi_graph(i);
  }
 return 0;
}