void CanvasPartition(TCanvas *C,const Int_t Nx = 2,const Int_t Ny = 2,
                     Float_t lMargin = 0.15, Float_t rMargin = 0.05,
                     Float_t bMargin = 0.15, Float_t tMargin = 0.05);

void canvas3()
{

   gStyle->SetOptStat(0);

   TCanvas *C = (TCanvas*) gROOT->FindObject("C");
   if (C) delete C;
   C = new TCanvas("C","canvas",1024,640);
   C->SetFillStyle(4000);

   // Number of PADS
   const Int_t Nx = 3;
   const Int_t Ny = 1;

   // Margins
   Float_t lMargin = 0.12;
   Float_t rMargin = 0.05;
   Float_t bMargin = 0.15;
   Float_t tMargin = 0.05;

   // Canvas setup
   CanvasPartition(C,Nx,Ny,lMargin,rMargin,bMargin,tMargin);

   // Dummy histogram.
   TH1F *h = (TH1F*) gROOT->FindObject("histo");
   if (h) delete h;
   h = new TH1F("histo","",100,0.,5.);
   h->FillRandom("gaus",10000);
   h->GetXaxis()->SetTitle("x axis");
   h->GetYaxis()->SetTitle("y axis");

   TPad *pad[Nx][Ny];

   for (Int_t i=0;i<Nx;i++) {
      for (Int_t j=0;j<Ny;j++) {
         C->cd(0);

         // Get the pads previously created.
         char pname[16];
         sprintf(pname,"pad_%i_%i",i,j);
         pad[i][j] = (TPad*) gROOT->FindObject(pname);
         pad[i][j]->Draw();
         pad[i][j]->SetFillStyle(0);
         pad[i][j]->SetFrameFillStyle(0);
         pad[i][j]->cd();

         // Size factors
         Float_t xFactor = pad[0][0]->GetAbsWNDC()/pad[i][j]->GetAbsWNDC();
         Float_t yFactor = pad[0][0]->GetAbsHNDC()/pad[i][j]->GetAbsHNDC();

         char hname[16];
         sprintf(hname,"h_%i_%i",i,j);
         TH1F *hFrame = (TH1F*) h->Clone(hname);
         hFrame->Reset();
         hFrame->Draw();
         hFrame->GetXaxis()->ChangeLabel(1,-1,0.); // remove the first label
         hFrame->GetXaxis()->ChangeLabel(-1,-1,0.); // remove the last label

         // y axis range
         hFrame->GetYaxis()->SetRangeUser(0.0001,1.2*h->GetMaximum());

         // Format for y axis
         hFrame->GetYaxis()->SetLabelFont(43);
         hFrame->GetYaxis()->SetLabelSize(16);
         hFrame->GetYaxis()->SetLabelOffset(0.02);
         hFrame->GetYaxis()->SetTitleFont(43);
         hFrame->GetYaxis()->SetTitleSize(16);
         hFrame->GetYaxis()->SetTitleOffset(5);

         hFrame->GetYaxis()->CenterTitle();
         hFrame->GetYaxis()->SetNdivisions(505);

         // TICKS Y Axis
         hFrame->GetYaxis()->SetTickLength(xFactor*0.04/yFactor);

         // Format for x axis
         hFrame->GetXaxis()->SetLabelFont(43);
         hFrame->GetXaxis()->SetLabelSize(16);
         hFrame->GetXaxis()->SetLabelOffset(0.02);
         hFrame->GetXaxis()->SetTitleFont(43);
         hFrame->GetXaxis()->SetTitleSize(16);
         hFrame->GetXaxis()->SetTitleOffset(5);
         hFrame->GetXaxis()->CenterTitle();
         hFrame->GetXaxis()->SetNdivisions(505);

         // TICKS X Axis
         hFrame->GetXaxis()->SetTickLength(yFactor*0.06/xFactor);

         h->Draw("same");
      }
   }
   C->cd();
}



void CanvasPartition(TCanvas *C,const Int_t Nx,const Int_t Ny,
                     Float_t lMargin, Float_t rMargin,
                     Float_t bMargin, Float_t tMargin)
{
   if (!C) return;

   // Setup Pad layout:
   Float_t vSpacing = 0.0;
   Float_t vStep  = (1.- bMargin - tMargin - (Ny-1) * vSpacing) / Ny;

   Float_t hSpacing = 0.0;
   Float_t hStep  = (1.- lMargin - rMargin - (Nx-1) * hSpacing) / Nx;

   Float_t vposd,vposu,vmard,vmaru,vfactor;
   Float_t hposl,hposr,hmarl,hmarr,hfactor;

   for (Int_t i=0;i<Nx;i++) {

      if (i==0) {
         hposl = 0.0;
         hposr = lMargin + hStep;
         hfactor = hposr-hposl;
         hmarl = lMargin / hfactor;
         hmarr = 0.0;
      } else if (i == Nx-1) {
         hposl = hposr + hSpacing;
         hposr = hposl + hStep + rMargin;
         hfactor = hposr-hposl;
         hmarl = 0.0;
         hmarr = rMargin / (hposr-hposl);
      } else {
         hposl = hposr + hSpacing;
         hposr = hposl + hStep;
         hfactor = hposr-hposl;
         hmarl = 0.0;
         hmarr = 0.0;
      }

      for (Int_t j=0;j<Ny;j++) {

         if (j==0) {
            vposd = 0.0;
            vposu = bMargin + vStep;
            vfactor = vposu-vposd;
            vmard = bMargin / vfactor;
            vmaru = 0.0;
         } else if (j == Ny-1) {
            vposd = vposu + vSpacing;
            vposu = vposd + vStep + tMargin;
            vfactor = vposu-vposd;
            vmard = 0.0;
            vmaru = tMargin / (vposu-vposd);
         } else {
            vposd = vposu + vSpacing;
            vposu = vposd + vStep;
            vfactor = vposu-vposd;
            vmard = 0.0;
            vmaru = 0.0;
         }

         C->cd(0);

         char name[16];
         sprintf(name,"pad_%i_%i",i,j);
         TPad *pad = (TPad*) gROOT->FindObject(name);
         if (pad) delete pad;
         pad = new TPad(name,"",hposl,vposd,hposr,vposu);
         pad->SetLeftMargin(hmarl);
         pad->SetRightMargin(hmarr);
         pad->SetBottomMargin(vmard);
         pad->SetTopMargin(vmaru);

         pad->SetFrameBorderMode(0);
         pad->SetBorderMode(0);
         pad->SetBorderSize(0);

         pad->Draw();
      }
   }
}