rf301_composition.C

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/// \file
/// \ingroup tutorial_roofit
/// \notebook
///  'MULTIDIMENSIONAL MODELS' RooFit tutorial macro #301
///
///  Multi-dimensional p.d.f.s through composition, e.g. substituting a
///  p.d.f parameter with a function that depends on other observables
///
///  pdf = gauss(x,f(y),s) with f(y) = a0 + a1*y
///
/// \macro_image
/// \macro_output
/// \macro_code
/// \author 07/2008 - Wouter Verkerke


#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooPolyVar.h"
#include "RooPlot.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "TH1.h"
using namespace RooFit ;



void rf301_composition()
{
   // S e t u p   c o m p o s e d   m o d e l   g a u s s ( x , m ( y ) , s )
   // -----------------------------------------------------------------------

   // Create observables
   RooRealVar x("x","x",-5,5) ;
   RooRealVar y("y","y",-5,5) ;

   // Create function f(y) = a0 + a1*y
   RooRealVar a0("a0","a0",-0.5,-5,5) ;
   RooRealVar a1("a1","a1",-0.5,-1,1) ;
   RooPolyVar fy("fy","fy",y,RooArgSet(a0,a1)) ;

   // Create gauss(x,f(y),s)
   RooRealVar sigma("sigma","width of gaussian",0.5) ;
   RooGaussian model("model","Gaussian with shifting mean",x,fy,sigma) ;


   // S a m p l e   d a t a ,   p l o t   d a t a   a n d   p d f   o n   x   a n d   y
   // ---------------------------------------------------------------------------------

   // Generate 10000 events in x and y from model
   RooDataSet *data = model.generate(RooArgSet(x,y),10000) ;

   // Plot x distribution of data and projection of model on x = Int(dy) model(x,y)
   RooPlot* xframe = x.frame() ;
   data->plotOn(xframe) ;
   model.plotOn(xframe) ;

   // Plot x distribution of data and projection of model on y = Int(dx) model(x,y)
   RooPlot* yframe = y.frame() ;
   data->plotOn(yframe) ;
   model.plotOn(yframe) ;

   // Make two-dimensional plot in x vs y
   TH1* hh_model = model.createHistogram("hh_model",x,Binning(50),YVar(y,Binning(50))) ;
   hh_model->SetLineColor(kBlue) ;



   // Make canvas and draw RooPlots
   TCanvas *c = new TCanvas("rf301_composition","rf301_composition",1200, 400);
   c->Divide(3);
   c->cd(1) ; gPad->SetLeftMargin(0.15) ; xframe->GetYaxis()->SetTitleOffset(1.4) ; xframe->Draw() ;
   c->cd(2) ; gPad->SetLeftMargin(0.15) ; yframe->GetYaxis()->SetTitleOffset(1.4) ; yframe->Draw() ;
   c->cd(3) ; gPad->SetLeftMargin(0.20) ; hh_model->GetZaxis()->SetTitleOffset(2.5) ; hh_model->Draw("surf") ;

}