Double_t fitf(Double_t *x, Double_t *par) 
{ 
   return par[0]*exp(-1*20e-9*x[0]*par[1]); 
} 

Double_t ftotal(Double_t *x, Double_t *par) 
{ 
  return fitf(x,par) + fitf(x,&par[4]); 
} 

void myfit() 
{ 

  gROOT->Reset();
  gStyle->SetOptFit();


  TH1F *h = (TH1F *) gROOT->FindObject("histup");
  if (h) h->Delete();

  TH1F *h = (TH1F *) gROOT->FindObject("histup2");
  if (h) h->Delete();


  Double_t par[6];

  TFile *file = new TFile("spike_data.root","update");

  TCanvas *c1 = new TCanvas("c1", "Spike data", 0, 0, 700, 700);
  c1->Divide(0,2);
  c1->cd(1);


  TH1F *histup = new TH1F("histup", "Up Decay Histogram", 291,10,300);
  spike_data_UP->Draw("UP_time >> histup");



  /*
    Defining the various fit functions and their ranges
  */  
  TF1 *g1 = new TF1("Fit1", fitf,10,28,2); 
  TF1 *g2 = new TF1("Fit2", fitf,35,300, 2); 
  total = new TF1("mstotal",ftotal,10,316,4); 

  g1->SetLineColor(kRed);
  g2->SetLineColor(kGreen);

  histup->Fit(g1,"R");
  histup->Fit(g2,"R+"); 
   
  g1->GetParameters(&par[0]); 
  g2->GetParameters(&par[2]); 

  total->SetParameters(par); 
  total->SetLineColor(kBlue);
  total->SetParLimits(1, 33333, 1e6);
  total->SetParLimits(3, 33333, 1e6);


  histup->Fit(total,"R+"); 

  double ChiSq = mstotal->GetChisquare();
  double NDF = mstotal->GetNDF();

  printf("ChiSq/NDF: %.2f\n",ChiSq/NDF);
    
  c1->cd(2);

  TH1F *histup2 = new TH1F("histup2", "Up Decay  Histogram (Edited)", 291,10,300);
  spike_data_UP->Draw("UP_time >> histup2");

  /*
    Setting the bin contents of where the spike is to more "appropriate" values
  */

  histup2->SetBinContent(18, 150);
  histup2->SetBinContent(19, 145);
  histup2->SetBinContent(20, 143);
  histup2->SetBinContent(21, 136);
  histup2->SetBinContent(22, 130);
  histup2->SetBinContent(23, 127);
  histup2->SetBinContent(24, 130);
  histup2->SetBinContent(25, 125);

  histup2->Draw();

  TF1 *g1 = new TF1("Fit1", fitf,10,28,2); 
  TF1 *g2 = new TF1("Fit2", fitf,35,300, 2); 
  total = new TF1("mstotal",ftotal,10,316,4); 

  g1->SetLineColor(kRed);
  g2->SetLineColor(kGreen);

  histup2->Fit(g1,"R");
  histup2->Fit(g2,"R+"); 
   
  g1->GetParameters(&par[0]); 
  g2->GetParameters(&par[2]); 

  total->SetParameters(par); 
  total->SetLineColor(kBlue);
  total->SetParLimits(1, 33333, 1e6);
  total->SetParLimits(3, 33333, 1e6);


  histup2->Fit(total,"R+"); 

  double ChiSq = mstotal->GetChisquare();
  double NDF = mstotal->GetNDF();

  printf("ChiSq/NDF: %.2f\n",ChiSq/NDF);
    
    
}