void ivcurve2()
{

  
  gROOT->SetBatch(kTRUE);
  gStyle->SetOptStat(0);
  gStyle->SetOptTitle(0);
  gStyle->SetTitleSize(0.05,"XY");
  gStyle->SetTitleOffset(.9, "XY");
  gStyle->SetStatY(0.9); 
  gStyle->SetStatX(0.9);

  TCanvas *c1 = new TCanvas("c1", "c1",18,41,700,500);
   c1->Range(24,50,40,70);


  hDummy = new TH2D("hDummy","hDummy",1000,0,80,1000,0,3);
  hDummy->Draw("axis");
  hDummy->GetXaxis()->SetTitle("Voltage [V]");
  hDummy->GetYaxis()->SetTitle("Current [A]");
  hDummy->GetXaxis()->CenterTitle();
  hDummy->GetYaxis()->CenterTitle();
  const Int_t n = 4;
                         
        //Setting data for voltage and current
  Float_t voltage[n] = {5.0456,6.625,10.9227,15.0141};
  Float_t current[n] = {0.1315,0.23,0.5317,0.8374};
  Float_t currentI[n] = {};
    float currentNaturalLog = 0.0; 
    for (int i = 0; i < n; i++)  
        currentNaturalLog =  log(current[i]); 
//Finding the derivative for current.
double x1 = currentNaturalLog[0]
double x2 = currentNaturalLog[1]-currentNaturalLog[0]
double x3 = currentNaturalLog[2]-currentNaturalLog[1]
double x4 = currentNaturalLog[3]-currentNaturalLog[2]
double x5 = currentNaturalLog[4]-currentNaturalLog[3]
double x6 = currentNaturalLog[5]-currentNaturalLog[4]

//Finding the derivative of voltage
double v1 = voltage[0]
v2 = voltage[1]-voltage[0]
v3 = voltage[2]-voltage[1]
v4 = voltage[3]-voltage[2]
v5 = voltage[4]-voltage[3]
v6 = voltage[5]-voltage[4]

float dNaturallogI[n] = {x1,x2,x3,x4,x5,x6}
float dV[n] = {v1,v2,v3,v4,v5,v6}

  TGraph *iv_curve = new TGraph(n,voltage,current);
  iv_curve->SetMarkerStyle(20);
  iv_curve->SetMarkerColor(kRed);
  iv_curve->Draw("p same");

  TF1 *iv_curvefit = new TF1("iv_curvefit","[0]+x*[1]",0,1);
  iv_curvefit->SetLineColor(kRed);
  iv_curve->Fit("iv_curvefit");


  ///TImage *img = TImage::Create();

   ///img->FromPad(c1, 10, 10, 300, 200);
   ///img->FromPad(c1);

   ///img->WriteImage("ivcurve.png");
}