void projxy(TH2 * h2in = NULL){

   TH2 * hist = h2in;
   if(hist == NULL){
//  generate a sample hist
      TH2F * hdummy = new TH2F("gvsg", "gaus vs gaus", 40,-4, 4, 40,-2, 6);
      Double_t px, py;
      for(Int_t i=0; i<10000; i++){
         gRandom->Rannor(px,py);
         hdummy->Fill(px, 0.9*py );
         gRandom->Rannor(px,py);
         hdummy->Fill(px, 0.6*py + 4);
      }
      hist = hdummy;
   }
//  set parameters / options, could be done outside 
   Bool_t logZscale = kFALSE;
   Bool_t logXscale = kFALSE;
   Bool_t logYscale = kFALSE;

   TString option_2dim("COLz");

   TString option_1dim("H");                   // options for the 1-dim hists
   TString option_1dim_y(option_1dim.Data());  // y-projection is a TGraph
                                               // which has diff options
   Int_t marker_style = TAttMarker::kStar;

   TString fill_option("F");    
   Int_t fill_style = 1001;
   Int_t fill_color = 45;

   Double_t x2dim = 0.5;        // the space left for the 2dim hist x
   Double_t y2dim = 0.5;        // the space left for the 2dim hist y
   Double_t sep = 0.005;        // the space between pads

   gStyle->SetPalette(1,0);     // violet - red 

   Int_t ww = 900;              // dimensions for the canvas
   Int_t wh = 900;
   Int_t wtopx = 800;
   Int_t wtopy = 20;

//  Need a canvas + 3 pads 

   TCanvas * cHist = new TCanvas("forall", "forall", wtopx, wtopy, ww, wh);

   if(option_1dim.Length() == 0)option_1dim = "HIST";
   if(x2dim > 1 || x2dim <= 0)x2dim = 0.5;
   if(y2dim > 1 || y2dim <= 0)y2dim = 0.5;

   TPad * pad2dim = new TPad("pad2dim","pad2dim",0,0, x2dim-sep, y2dim-sep);
   pad2dim->Draw();
   pad2dim->cd();
   hist->Draw(option_2dim.Data());
   cHist->cd();
   TPad * padprojx = new TPad("padprojx", "padprojx", 0, y2dim+sep, x2dim-sep, 1);
   padprojx->Draw();
   cHist->cd();
   TPad * padprojy = new TPad("padprojy", "padprojy", x2dim+sep, 0, 1, y2dim-sep);
   padprojy->Draw();
   cHist->cd();
//  for test only, may be used for the y-projection
   TPad * padprojxy = new TPad("padprojxy", "padprojxy", x2dim+sep, y2dim+sep, 1, 1);
   padprojxy->Draw();

   if(logZscale){
      pad2dim->SetLogz();
      padprojx->SetLogy();
      padprojy->SetLogx();
      padprojxy->SetLogy();
   }
   if(logXscale){;
      pad2dim->SetLogx();
      padprojx->SetLogx();
   }
   if(logYscale){
      pad2dim->SetLogy();
      padprojy->SetLogy();
   }
   gStyle->SetOptStat(0);
   if(option_1dim.Contains("P", TString::kIgnoreCase))
     gStyle->SetMarkerStyle(marker_style);
   else
     gStyle->SetMarkerStyle(0);

   Int_t nbins;
   Double_t x, y, dx2, dy2, err;
   TGraph * g;
   TGraphErrors * ge;

//  x-projection is simple

   TH1D * projHistX = hist->ProjectionX();
   padprojx->cd();
   if(fill_option.Contains("F", TString::kIgnoreCase)){
      projHistX->SetFillStyle(fill_style);
      projHistX->SetFillColor(fill_color);
   }
   projHistX->Draw("bar2");

//  y-projection drawn as a TGraphErrors

   TH1D * projHistY = hist->ProjectionY();
//  we might draw y-projection into unused space at upper right corner
   padprojxy->cd();
   if(fill_option.Contains("F", TString::kIgnoreCase)){
      projHistY->SetFillStyle(fill_style);
      projHistY->SetFillColor(fill_color);
   }
   projHistY->Draw("bar2");

   padprojy->cd();
   projHistY->Draw("hbar2");
}