{
#include <iostream>
#include <math.h>
// Electric field calculation,  Taka Kondo (KEK) 2009.11.27, modidied 2010.1.17
// unit: nsec, cm, sec, K, 
c1 = new TCanvas("c1","A Simple Graph with error bars",0,0,700,500);
c1->SetFillStyle(4100);
c1->SetGrid();
c1->GetFrame()->SetBorderSize(12);
double d = 0.0285;           // [cm]
double Vd = 65.0;            // [V] 
double Vb;                      // [V]
double Ey, Emax, y, wd;
int nhist=200;
double deltay=d/nhist;

TH1F *hE = new TH1F("hE","Electric field",nhist,0,d*10000.); 
for (int i=0; i<10 ;i++) {
   Vb=10.+20.*i;
   TH1F *h = new TH1F("h","Electric field",nhist,0,d*10000.); 
   for (y=deltay*0.5; y<d ; y+=deltay){
      if (Vb>Vd) {
           Emax = (Vb+Vd)/d ;
           //Ey = Emax - 2.*Vd*y/(d*d); //flat diode model
           Ey = Vb/d;                              //uniform field model
      } else {
           wd = sqrt(Vb/Vd) * d;
           Emax = 2.* wd * Vd /(d*d);  
           //Ey = Emax*(1-y/wd);   //flat diode model
           Ey = Vb/wd;                   //uniform field model
           if(y>wd) Ey=0.;                //uniform field model
      }
      if(i == 0) hE->Fill((d-y)*10000,Ey);
      else h->Fill((d-y)*10000., Ey);
   }
  gStyle->SetOptStat(0); 
  hE->SetMaximum(10000.);
  hE->SetMinimum(0.);
  hE->SetTitle();
  hE->SetXTitle("depth [#mum]");
  hE->SetYTitle("Electric Filed [V/cm]");
  hE->GetYaxis()->SetTitleOffset(1.5);
  hE->GetXaxis()->SetTitleOffset(1.0);
  if(Vb==150.) h->SetLineColor(2);
  if(i == 0) hE ->Draw("L");
  else h->Draw("SAME L");    
}
b = new TBox(75., 8900., 220., 9600.); 
b->SetFillColor(10); b->Draw(); 
TLatex *t=new TLatex(80., 9100.,"Uniform field model (V_{D} = 65 V)");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(225., 1000.,"10 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(225., 1600.,"30 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(225., 2050.,"50 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(225., 2550.,"70 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(225., 3250.,"90 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(220., 4000.,"110 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(220., 4700.,"130 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(220., 5400.,"150 V");t->SetTextSize(0.04); 
t->SetTextColor(2);t->Draw();
TLatex *t=new TLatex(220., 6100.,"170 V");t->SetTextSize(0.04); t->Draw();
TLatex *t=new TLatex(200., 6850.,"V_{B} = 190 V");t->SetTextSize(0.04); t->Draw();
}