#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "TCanvas.h"
#include "RooPlot.h"
#include "TAxis.h"
using namespace RooFit;
 
void test_shiftRooKey()
{
   // S e t u p   m o d e l
   // ---------------------
 
   // Declare variables x,mean,sigma with associated name, title, initial value and allowed range
   RooRealVar x("x", "x", 0,  -10, 10);
   RooRealVar shift( "shift", "shift" , 0, -10,10);
   RooRealVar mean("mean", "mean of gaussian", 0, -10, 10);
   RooRealVar sigma("sigma", "width of gaussian", 3, 0.1, 10);
   RooRealVar shiftPar("shift", "shift", 0, -20, 20);
   RooFormulaVar shiftMean( "shiftMean", "@0-@1", RooArgList(x, shiftPar));
   RooGaussian gauss("gauss", "gaussian PDF", x, mean, sigma);
   RooPlot *xframe = x.frame(Title("Gaussian pdf."));
   // P l o t   m o d e l   used to generate 
   // ---------------------------------------------------------------------------
   gauss.plotOn(xframe);
   gauss.plotOn(xframe, LineColor(kRed));
   RooDataSet *data = gauss.generate(x, 10000);
   //make a RooKeyPdf on the x, and passing the shiftedX par 
   RooKeysPdf rookeyNotShift("myRooKey", "myRooKey", shiftMean, x, *data); 
   //plot the RooKeyPdf with "no-shift" in place obtained from generated centered gaussian
   rookeyNotShift.plotOn(xframe,LineColor(kGray));
   //shift the gaussian by 3 units, to fit the RooKeyAfterwards
   mean.setVal(3);
   RooDataSet *data_shifted = gauss.generate(x, 10000);

   //Make the second plot 
   RooPlot *xframe2 = x.frame(Title("RooKey with the shift applied fit"));
   data_shifted->plotOn(xframe2,LineColor(kRed));
   
   rookeyNotShift.fitTo( *data_shifted);
   rookeyNotShift.plotOn( xframe2);
   // Print values of mean and sigma (that now reflect fitted values and errors)
   mean.Print();
   shiftPar.Print();
   sigma.Print();
   // Draw all frames on a canvas
   TCanvas *c = new TCanvas("rf101_basics", "rf101_basics", 800, 400);
   c->Divide(2);
   c->cd(1);
   gPad->SetLeftMargin(0.15);
   xframe->GetYaxis()->SetTitleOffset(1.6);
   xframe->Draw();
   c->cd(2);
   gPad->SetLeftMargin(0.15);
   xframe2->GetYaxis()->SetTitleOffset(1.6);
   xframe2->Draw();
}