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Reference Guide
RooChiSquarePdf.cxx
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1/*****************************************************************************
2 * Project: RooFit *
3 * Package: RooFitModels *
4 * @(#)root/roofit:$Id$
5 * Authors: *
6 * Kyle Cranmer
7 * *
8 *****************************************************************************/
9
10/** \class RooChiSquarePdf
11 \ingroup Roofit
12
13The PDF of the Chi Square distribution for n degrees of freedom.
14Oddly, this is hard to find in ROOT (except via relation to GammaDist).
15Here we also implement the analytic integral.
16**/
17
18#include "RooChiSquarePdf.h"
19#include "RooFit.h"
20#include "RooAbsReal.h"
21#include "RooRealVar.h"
22#include "RooBatchCompute.h"
23
24#include "TMath.h"
25
26#include <cmath>
27using namespace std;
28
30
31////////////////////////////////////////////////////////////////////////////////
32
34{
35}
36
37////////////////////////////////////////////////////////////////////////////////
38
39RooChiSquarePdf::RooChiSquarePdf(const char* name, const char* title,
40 RooAbsReal& x, RooAbsReal& ndof):
41 RooAbsPdf(name, title),
42 _x("x", "Dependent", this, x),
43 _ndof("ndof","ndof", this, ndof)
44{
45}
46
47////////////////////////////////////////////////////////////////////////////////
48
50 RooAbsPdf(other, name),
51 _x("x", this, other._x),
52 _ndof("ndof",this,other._ndof)
53{
54}
55
56////////////////////////////////////////////////////////////////////////////////
57
59{
60 if(_x <= 0) return 0;
61
62 return pow(_x,(_ndof/2.)-1.) * exp(-_x/2.) / TMath::Gamma(_ndof/2.) / pow(2.,_ndof/2.);
63}
64
65////////////////////////////////////////////////////////////////////////////////
66/// Compute multiple values of ChiSquare distribution.
67void RooChiSquarePdf::computeBatch(cudaStream_t* stream, double* output, size_t nEvents, RooBatchCompute::DataMap& dataMap) const
68{
70 dispatch->compute(stream, RooBatchCompute::ChiSquare, output, nEvents, dataMap, {&*_x,&*_norm}, {_ndof});
71}
72
73////////////////////////////////////////////////////////////////////////////////
74/// No analytical calculation available (yet) of integrals over subranges
75
76Int_t RooChiSquarePdf::getAnalyticalIntegral(RooArgSet& allVars, RooArgSet& analVars, const char* rangeName) const
77{
78 if (rangeName && strlen(rangeName)) {
79 return 0 ;
80 }
81
82 if (matchArgs(allVars, analVars, _x)) return 1;
83 return 0;
84}
85
86////////////////////////////////////////////////////////////////////////////////
87
88Double_t RooChiSquarePdf::analyticalIntegral(Int_t code, const char* rangeName) const
89{
90 assert(1 == code); (void)code;
91 Double_t xmin = _x.min(rangeName); Double_t xmax = _x.max(rangeName);
92
93 // TMath::Prob needs ndof to be an integer, or it returns 0.
94 // return TMath::Prob(xmin, _ndof) - TMath::Prob(xmax,_ndof);
95
96 // cumulative is known based on lower incomplete gamma function, or regularized gamma function
97 // Wikipedia defines lower incomplete gamma function without the normalization 1/Gamma(ndof),
98 // but it is included in the ROOT implementation.
99 Double_t pmin = TMath::Gamma(_ndof/2,xmin/2);
100 Double_t pmax = TMath::Gamma(_ndof/2,xmax/2);
101
102 // only use this if range is appropriate
103 return pmax-pmin;
104}
typedef void(GLAPIENTRYP _GLUfuncptr)(void)
#define ClassImp(name)
Definition: Rtypes.h:364
char name[80]
Definition: TGX11.cxx:110
float xmin
Definition: THbookFile.cxx:95
float xmax
Definition: THbookFile.cxx:95
RooAbsReal * _norm
Definition: RooAbsPdf.h:364
RooAbsReal is the common abstract base class for objects that represent a real value and implements f...
Definition: RooAbsReal.h:63
Bool_t matchArgs(const RooArgSet &allDeps, RooArgSet &numDeps, const RooArgProxy &a) const
Utility function for use in getAnalyticalIntegral().
RooArgSet is a container object that can hold multiple RooAbsArg objects.
Definition: RooArgSet.h:35
virtual void compute(cudaStream_t *, Computer, RestrictArr, size_t, const DataMap &, const VarVector &, const ArgVector &={})=0
The PDF of the Chi Square distribution for n degrees of freedom.
Double_t evaluate() const
Evaluate this PDF / function / constant. Needs to be overridden by all derived classes.
void computeBatch(cudaStream_t *, double *output, size_t nEvents, RooBatchCompute::DataMap &) const
Compute multiple values of ChiSquare distribution.
Double_t analyticalIntegral(Int_t code, const char *rangeName=0) const
Implements the actual analytical integral(s) advertised by getAnalyticalIntegral.
RooRealProxy _ndof
Int_t getAnalyticalIntegral(RooArgSet &allVars, RooArgSet &analVars, const char *rangeName=0) const
No analytical calculation available (yet) of integrals over subranges.
RooRealProxy _x
double min(const char *rname=0) const
Query lower limit of range. This requires the payload to be RooAbsRealLValue or derived.
double max(const char *rname=0) const
Query upper limit of range. This requires the payload to be RooAbsRealLValue or derived.
Double_t x[n]
Definition: legend1.C:17
R__EXTERN RooBatchComputeInterface * dispatchCUDA
std::map< DataKey, RooSpan< const double > > DataMap
R__EXTERN RooBatchComputeInterface * dispatchCPU
This dispatch pointer points to an implementation of the compute library, provided one has been loade...
Double_t Gamma(Double_t z)
Computation of gamma(z) for all z.
Definition: TMath.cxx:348
static void output(int code)
Definition: gifencode.c:226