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);
double XtoPad(double x);
double YtoPad(double x);

void canvas2()
{
   gStyle->SetOptStat(0);

   auto 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 = 5;
   const Int_t Ny = 5;

   // 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.
   auto h = (TH1F *)gROOT->FindObject("histo");
   if (h)
      delete h;
   h = new TH1F("histo", "", 100, -5.0, 5.0);
   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.
         pad[i][j] = (TPad *)C->FindObject(TString::Format("pad_%d_%d", i, j).Data());
         pad[i][j]->Draw();
         pad[i][j]->SetFillStyle(4000);
         pad[i][j]->SetFrameFillStyle(4000);
         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();

         TH1F *hFrame = (TH1F *)h->Clone(TString::Format("h_%d_%d", i, j).Data());

         // y axis range
         hFrame->SetMinimum(0.0001); // do not show 0
         hFrame->SetMaximum(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(2);

         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(1);
         hFrame->GetXaxis()->CenterTitle();
         hFrame->GetXaxis()->SetNdivisions(505);

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

         // Draw cloned histogram with individual settings
         hFrame->Draw();

         TText text;
         text.SetTextAlign(31);
         text.SetTextFont(43);
         text.SetTextSize(10);
         text.DrawTextNDC(XtoPad(0.9), YtoPad(0.8), gPad->GetName());
      }
   }
   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);

         auto name = TString::Format("pad_%d_%d", i, j);
         auto pad = (TPad *)C->FindObject(name.Data());
         if (pad)
            delete pad;
         pad = new TPad(name.Data(), "", 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();
      }
   }
}

double XtoPad(double x)
{
   double xl, yl, xu, yu;
   gPad->GetPadPar(xl, yl, xu, yu);
   double pw = xu - xl;
   double lm = gPad->GetLeftMargin();
   double rm = gPad->GetRightMargin();
   double fw = pw - pw * lm - pw * rm;
   return (x * fw + pw * lm) / pw;
}

double YtoPad(double y)
{
   double xl, yl, xu, yu;
   gPad->GetPadPar(xl, yl, xu, yu);
   double ph = yu - yl;
   double tm = gPad->GetTopMargin();
   double bm = gPad->GetBottomMargin();
   double fh = ph - ph * bm - ph * tm;
   return (y * fh + bm * ph) / ph;
}