// rangauss2d.C : generate correlated random gaussian numbers 
//
#include <iostream>
#include <TH1.h>
#include <TF1.h>
#include <TText.h>
#include <TCanvas.h>
#include <TSystem.h>
#include <TRandom.h>
#include <TStyle.h>

int rangauss2d(const int Nrndm=500, const int Nfill=100) 
{ 

// * define some constants
//const int Nrndm=2;   // fill one random number each time
//const int Nfill=1000; // number of times to fill histogram
const int Nbinsx=50;
const double xmin=-3.9;
const double xmax=3.9;
const int Nbinsy=50;
const double ymin=-3.9;
const double ymax=3.9;

const double mux=0.;
const double muy=0.;
const double sigx=1.;
const double sigy=1.;
const double rho=0.75;

double u1,u2,x,y;

// initialze Random Generator
 TRandom3 myrnd;

// ----------------------------------------------------------------

// create main canvas
//                                                    at xtop ytop sizex sizey
 TCanvas *theCanvas=new TCanvas("theCanvas","TestCanvas", 100, 100, 540, 600);
 TPad *txtPad = new TPad("txtPad","TextPad",0.,0.9,1.,1.);
 TPad *hstPad = new TPad("hstPad","HistPad",0.,0. ,1.,0.9);
 txtPad->Draw();
 hstPad->Draw();

// set active pad to text pad and print some text
txtPad->cd();
gPad->SetFillColor(42); 
gStyle->SetTextColor(9);
char txt[50];
 sprintf(txt,"mux=%1.2f, sigx=%1.2f, muy=%1.2f, sigy=%1.2f, rho=%1.2f"
   ,mux,sigx,muy,sigy,rho);
TText* txtHead= new TText(0.1,0.7, const_cast<char*>(txt)); 
txtHead->SetTextSize(0.3);
txtHead->Draw();


// text for output
gStyle->SetTextColor(1); // text color black
TText* txtResult= new TText(); 
txtResult->SetTextSize(0.3);

// some histogram style options
gStyle->SetHistLineColor(46); 
gStyle->SetHistFillColor(3);
gStyle->SetHistLineWidth(3);
gStyle->SetAxisColor(4,"X");
gStyle->SetAxisColor(4,"Y");
gStyle->SetLabelColor(4,"X");
gStyle->SetLabelColor(4,"Y");
gStyle->SetOptStat(1111);

// set active pad to graphics pad and define some colors
hstPad->cd();
gPad->SetFillColor(0); 
gPad->SetGrid();
 
// book a histogram, w. Nbins bins, range [xmin,xmax[
 TH2F* hxy =new TH2F("hxy","correlated random numbers"
                    ,Nbinsx,xmin,xmax,Nbinsy,ymin,ymax);
// fill random numbers in a loop , Nfill times, Nrndm at a time
for(int j =0; j<Nfill; j++) {
  for (int k=0; k<Nrndm;k++){
    u1=gRandom->Gaus(0.,1.); 
    u2=gRandom->Gaus(0.,1.);
    x=mux+sigx*u1; 
    y=muy+sigy*(rho*u1 + sqrt(1-rho*rho)*u2);
    hxy->Fill(x,y);
  }

 txtPad->cd();
 sprintf(txt,"measured correlation %1.3g",hxy->GetCorrelationFactor());
 txtResult->SetText(0.5,0.3,txt); 
 txtResult->Draw(); 

 hstPad->cd();
 hxy->Draw("surf3");
 hstPad->Update(); 
}

 // cout<< "weiter? "; cin >> i;
 // delete theCanvas;

return 0;
}