RooStats::SPlot Class Reference

A class to calculate "sWeights" used to create an "sPlot".

An sPlot can reweight a dataset to show different components (e.g. signal / background), but it doesn't use cuts, and therefore doesn't have to sort events into signal/background (or other) categories. Instead of assigning a category to each event in the dataset, all events are weighted. To compute the weights, a PDF with different components is analysed, and the weights are added to the dataset. When plotting the dataset with the weights of the signal or background components, the data looks like "signal", but all events in the dataset are used.

The result is similar to a likelihood projection plot, but without cuts.

Note

SPlot needs to fit the pdf to the data once, so make sure that all relevant fit arguments such as the fit range are passed in the constructor.

The code is based on `‘SPlot: A statistical tool to unfold data distributions,’' Nucl. Instrum. Meth. A 555, 356 (2005) [arXiv:physics/0402083].

Creating an SPlot

To use this class, you first must have a pdf that includes yield parameters for (possibly several) different species, for example a signal and background yield. Those yields must be of type RooRealVar / RooLinearVar (or anything that derives from RooAbsRealLValue). This is necessary because RooStats needs to be able to set the yields to 0 and 1 to probe the PDF. After constructing the s weights, the yields will be restored to their original values.

To create an instance of the SPlot, supply a data set, the pdf to analyse, and a list which parameters of the pdf are yields. The SPlot will calculate SWeights, and include these as columns in the RooDataSet. The dataset will have two additional columns for every yield with name "`<varname>`":

• L_<varname> is the the likelihood for each event, i.e., the pdf evaluated for the given value of the variable "varname".
• <varname>_sw is the value of the sWeight for the variable "varname" for each event.

In SPlot::SPlot(), one can choose whether columns should be added to an existing dataset or whether a copy of the dataset should be created.

Plotting s-weighted data

After computing the s weights, create a new dataset that uses the s weights of the variable of interest for weighting. If the yield parameter for signal was e.g. "signalYield", the dataset can be constructed as follows:

RooDataSet data_signal("<name>", "<title>", <dataWithSWeights>, <variables>, 0, "signalYield_sw");

A complete tutorial with an extensive model is rs301_splot.C

Using ratios as yield parameters

As mentioned, RooStats needs to be able to modify the yield parameters. That means that they have to be a RooRealVar of a RooLinearVar. This allows using ratio parameters as in the following example:

RooRealVar x("x", "observable", 0, 0, 20);
RooRealVar m("m", "mean", 5., -10, 10);
RooRealVar s("s", "sigma", 2., 0, 10);
RooGaussian gaus("gaus", "gaus", x, m, s);
 
RooRealVar a("a", "exp", -0.2, -10., 0.);
RooExponential ex("ex", "ex", x, a);
 
RooRealVar common("common", "common scale", 3., 0, 10);
RooRealVar r1("r1", "ratio of signal events", 0.3, 0, 10);
RooRealVar r2("r2", "ratio of background events", 0.5, 0, 10);
RooLinearVar c1("c1", "c1", r1, common, RooFit::RooConst(0.));
RooLinearVar c2("c2", "c2", r2, common, RooFit::RooConst(0.));
 
RooAddPdf sum("sum", "sum", RooArgSet(gaus, ex), RooArgSet(c1, c2));
auto data = sum.generate(x, 1000);
 
RooStats::SPlot splot("splot", "splot", *data, &sum, RooArgSet(c1, c2));

Definition at line 32 of file SPlot.h.

Public Member Functions
	SPlot ()
	Default constructor.
	SPlot (const char *name, const char *title)
	SPlot (const char *name, const char *title, const RooDataSet &data)
	Constructor from a RooDataSet No sWeighted variables are present.
	SPlot (const char *name, const char *title, RooDataSet &data, RooAbsPdf *pdf, const RooArgList &yieldsList, const RooArgSet &projDeps=RooArgSet(), bool useWeights=kTRUE, bool copyDataSet=kFALSE, const char *newName="", const RooCmdArg &fitToarg5=RooCmdArg::none(), const RooCmdArg &fitToarg6=RooCmdArg::none(), const RooCmdArg &fitToarg7=RooCmdArg::none(), const RooCmdArg &fitToarg8=RooCmdArg::none())
	Construct a new SPlot instance, calculate sWeights, and include them in the RooDataSet held by this instance.
	SPlot (const SPlot &other)
	Copy Constructor from another SPlot.
	~SPlot ()
void	AddSWeight (RooAbsPdf *pdf, const RooArgList &yieldsTmp, const RooArgSet &projDeps=RooArgSet(), bool includeWeights=kTRUE, const RooCmdArg &fitToarg5=RooCmdArg::none(), const RooCmdArg &fitToarg6=RooCmdArg::none(), const RooCmdArg &fitToarg7=RooCmdArg::none(), const RooCmdArg &fitToarg8=RooCmdArg::none())
	Method which adds the sWeights to the dataset.
Int_t	GetNumSWeightVars () const
	Return the number of SWeights In other words, return the number of species that we are trying to extract.
RooDataSet *	GetSDataSet () const
	Retrieve s-weighted data.
Double_t	GetSumOfEventSWeight (Int_t numEvent) const
	Sum the SWeights for a particular event.
Double_t	GetSWeight (Int_t numEvent, const char *sVariable) const
	Retrieve an s weight.
RooArgList	GetSWeightVars () const
	Return a RooArgList containing all paramters that have s weights.
Double_t	GetYieldFromSWeight (const char *sVariable) const
	Sum the SWeights for a particular species over all events.
RooDataSet *	SetSData (RooDataSet *data)
	Set dataset (if not passed in constructor).
Public Member Functions inherited from TNamed
	TNamed ()
	TNamed (const char *name, const char *title)
	TNamed (const TNamed &named)
	TNamed copy ctor.
	TNamed (const TString &name, const TString &title)
virtual	~TNamed ()
	TNamed destructor.
virtual void	Clear (Option_t *option="")
	Set name and title to empty strings ("").
virtual TObject *	Clone (const char *newname="") const
	Make a clone of an object using the Streamer facility.
virtual Int_t	Compare (const TObject *obj) const
	Compare two TNamed objects.
virtual void	Copy (TObject &named) const
	Copy this to obj.
virtual void	FillBuffer (char *&buffer)
	Encode TNamed into output buffer.
virtual const char *	GetName () const
	Returns name of object.
virtual const char *	GetTitle () const
	Returns title of object.
virtual ULong_t	Hash () const
	Return hash value for this object.
virtual Bool_t	IsSortable () const
virtual void	ls (Option_t *option="") const
	List TNamed name and title.
TNamed &	operator= (const TNamed &rhs)
	TNamed assignment operator.
virtual void	Print (Option_t *option="") const
	Print TNamed name and title.
virtual void	SetName (const char *name)
	Set the name of the TNamed.
virtual void	SetNameTitle (const char *name, const char *title)
	Set all the TNamed parameters (name and title).
virtual void	SetTitle (const char *title="")
	Set the title of the TNamed.
virtual Int_t	Sizeof () const
	Return size of the TNamed part of the TObject.
Public Member Functions inherited from TObject
	TObject ()
	TObject constructor.
	TObject (const TObject &object)
	TObject copy ctor.
virtual	~TObject ()
	TObject destructor.
void	AbstractMethod (const char *method) const
	Use this method to implement an "abstract" method that you don't want to leave purely abstract.
virtual void	AppendPad (Option_t *option="")
	Append graphics object to current pad.
virtual void	Browse (TBrowser *b)
	Browse object. May be overridden for another default action.
ULong_t	CheckedHash ()
	Check and record whether this class has a consistent Hash/RecursiveRemove setup (*) and then return the regular Hash value for this object.
virtual const char *	ClassName () const
	Returns name of class to which the object belongs.
virtual void	Delete (Option_t *option="")
	Delete this object.
virtual Int_t	DistancetoPrimitive (Int_t px, Int_t py)
	Computes distance from point (px,py) to the object.
virtual void	Draw (Option_t *option="")
	Default Draw method for all objects.
virtual void	DrawClass () const
	Draw class inheritance tree of the class to which this object belongs.
virtual TObject *	DrawClone (Option_t *option="") const
	Draw a clone of this object in the current selected pad for instance with: gROOT->SetSelectedPad(gPad).
virtual void	Dump () const
	Dump contents of object on stdout.
virtual void	Error (const char *method, const char *msgfmt,...) const
	Issue error message.
virtual void	Execute (const char *method, const char *params, Int_t *error=0)
	Execute method on this object with the given parameter string, e.g.
virtual void	Execute (TMethod *method, TObjArray *params, Int_t *error=0)
	Execute method on this object with parameters stored in the TObjArray.
virtual void	ExecuteEvent (Int_t event, Int_t px, Int_t py)
	Execute action corresponding to an event at (px,py).
virtual void	Fatal (const char *method, const char *msgfmt,...) const
	Issue fatal error message.
virtual TObject *	FindObject (const char *name) const
	Must be redefined in derived classes.
virtual TObject *	FindObject (const TObject *obj) const
	Must be redefined in derived classes.
virtual Option_t *	GetDrawOption () const
	Get option used by the graphics system to draw this object.
virtual const char *	GetIconName () const
	Returns mime type name of object.
virtual char *	GetObjectInfo (Int_t px, Int_t py) const
	Returns string containing info about the object at position (px,py).
virtual Option_t *	GetOption () const
virtual UInt_t	GetUniqueID () const
	Return the unique object id.
virtual Bool_t	HandleTimer (TTimer *timer)
	Execute action in response of a timer timing out.
Bool_t	HasInconsistentHash () const
	Return true is the type of this object is known to have an inconsistent setup for Hash and RecursiveRemove (i.e.
virtual void	Info (const char *method, const char *msgfmt,...) const
	Issue info message.
virtual Bool_t	InheritsFrom (const char *classname) const
	Returns kTRUE if object inherits from class "classname".
virtual Bool_t	InheritsFrom (const TClass *cl) const
	Returns kTRUE if object inherits from TClass cl.
virtual void	Inspect () const
	Dump contents of this object in a graphics canvas.
void	InvertBit (UInt_t f)
virtual Bool_t	IsEqual (const TObject *obj) const
	Default equal comparison (objects are equal if they have the same address in memory).
virtual Bool_t	IsFolder () const
	Returns kTRUE in case object contains browsable objects (like containers or lists of other objects).
R__ALWAYS_INLINE Bool_t	IsOnHeap () const
R__ALWAYS_INLINE Bool_t	IsZombie () const
void	MayNotUse (const char *method) const
	Use this method to signal that a method (defined in a base class) may not be called in a derived class (in principle against good design since a child class should not provide less functionality than its parent, however, sometimes it is necessary).
virtual Bool_t	Notify ()
	This method must be overridden to handle object notification.
void	Obsolete (const char *method, const char *asOfVers, const char *removedFromVers) const
	Use this method to declare a method obsolete.
void	operator delete (void *ptr)
	Operator delete.
void	operator delete[] (void *ptr)
	Operator delete [].
void *	operator new (size_t sz)
void *	operator new (size_t sz, void *vp)
void *	operator new[] (size_t sz)
void *	operator new[] (size_t sz, void *vp)
TObject &	operator= (const TObject &rhs)
	TObject assignment operator.
virtual void	Paint (Option_t *option="")
	This method must be overridden if a class wants to paint itself.
virtual void	Pop ()
	Pop on object drawn in a pad to the top of the display list.
virtual Int_t	Read (const char *name)
	Read contents of object with specified name from the current directory.
virtual void	RecursiveRemove (TObject *obj)
	Recursively remove this object from a list.
void	ResetBit (UInt_t f)
virtual void	SaveAs (const char *filename="", Option_t *option="") const
	Save this object in the file specified by filename.
virtual void	SavePrimitive (std::ostream &out, Option_t *option="")
	Save a primitive as a C++ statement(s) on output stream "out".
void	SetBit (UInt_t f)
void	SetBit (UInt_t f, Bool_t set)
	Set or unset the user status bits as specified in f.
virtual void	SetDrawOption (Option_t *option="")
	Set drawing option for object.
virtual void	SetUniqueID (UInt_t uid)
	Set the unique object id.
virtual void	SysError (const char *method, const char *msgfmt,...) const
	Issue system error message.
R__ALWAYS_INLINE Bool_t	TestBit (UInt_t f) const
Int_t	TestBits (UInt_t f) const
virtual void	UseCurrentStyle ()
	Set current style settings in this object This function is called when either TCanvas::UseCurrentStyle or TROOT::ForceStyle have been invoked.
virtual void	Warning (const char *method, const char *msgfmt,...) const
	Issue warning message.
virtual Int_t	Write (const char *name=0, Int_t option=0, Int_t bufsize=0)
	Write this object to the current directory.
virtual Int_t	Write (const char *name=0, Int_t option=0, Int_t bufsize=0) const
	Write this object to the current directory.

Protected Types
enum	{ kOwnData = BIT(20) }
Protected Types inherited from TObject
enum	{ kOnlyPrepStep = BIT(3) }

Protected Attributes
RooDataSet *	fSData
RooArgList	fSWeightVars
Protected Attributes inherited from TNamed
TString	fName
TString	fTitle

Additional Inherited Members
Public Types inherited from TObject
enum	{   kIsOnHeap = 0x01000000 , kNotDeleted = 0x02000000 , kZombie = 0x04000000 , kInconsistent = 0x08000000 ,   kBitMask = 0x00ffffff }
enum	{ kSingleKey = BIT(0) , kOverwrite = BIT(1) , kWriteDelete = BIT(2) }
enum	EDeprecatedStatusBits { kObjInCanvas = BIT(3) }
enum	EStatusBits {   kCanDelete = BIT(0) , kMustCleanup = BIT(3) , kIsReferenced = BIT(4) , kHasUUID = BIT(5) ,   kCannotPick = BIT(6) , kNoContextMenu = BIT(8) , kInvalidObject = BIT(13) }
Static Public Member Functions inherited from TObject
static Long_t	GetDtorOnly ()
	Return destructor only flag.
static Bool_t	GetObjectStat ()
	Get status of object stat flag.
static void	SetDtorOnly (void *obj)
	Set destructor only flag.
static void	SetObjectStat (Bool_t stat)
	Turn on/off tracking of objects in the TObjectTable.
Protected Member Functions inherited from TObject
virtual void	DoError (int level, const char *location, const char *fmt, va_list va) const
	Interface to ErrorHandler (protected).
void	MakeZombie ()

#include <RooStats/SPlot.h>

Inheritance diagram for RooStats::SPlot:

Member Enumeration Documentation

anonymous enum

anonymous enum

protected

Enumerator
kOwnData

Definition at line 74 of file SPlot.h.

Constructor & Destructor Documentation

~SPlot()

SPlot::~SPlot

(

)

Definition at line 120 of file SPlot.cxx.

SPlot() [1/5]

SPlot::SPlot

(

)

Default constructor.

Definition at line 130 of file SPlot.cxx.

SPlot() [2/5]

SPlot::SPlot

(

const SPlot &

other

)

Copy Constructor from another SPlot.

Definition at line 171 of file SPlot.cxx.

SPlot() [3/5]

SPlot::SPlot	(	const char *	name,
		const char *	title
	)

Definition at line 143 of file SPlot.cxx.

SPlot() [4/5]

SPlot::SPlot	(	const char *	name,
		const char *	title,
		const RooDataSet &	data
	)

Constructor from a RooDataSet No sWeighted variables are present.

Definition at line 158 of file SPlot.cxx.

SPlot() [5/5]

SPlot::SPlot	(	const char *	name,
		const char *	title,
		RooDataSet &	data,
		RooAbsPdf *	pdf,
		const RooArgList &	yieldsList,
		const RooArgSet &	projDeps = RooArgSet(),
		bool	useWeights = kTRUE,
		bool	cloneData = kFALSE,
		const char *	newName = "",
		const RooCmdArg &	arg5 = RooCmdArg::none(),
		const RooCmdArg &	arg6 = RooCmdArg::none(),
		const RooCmdArg &	arg7 = RooCmdArg::none(),
		const RooCmdArg &	arg8 = RooCmdArg::none()
	)

Construct a new SPlot instance, calculate sWeights, and include them in the RooDataSet held by this instance.

The constructor automatically calls AddSWeight() to add s weights to the dataset. These can be retrieved later using GetSWeight() or GetSDataSet().

Parameters

[in]	name	Name of the instance.
[in]	title	Title of the instance.
[in]	data	Dataset to fit to.
[in]	pdf	PDF to compute s weights for.
[in]	yieldsList	List of parameters in pdf that are yields. These must be RooRealVar or RooLinearVar, since RooStats will need to modify their values.
[in]	projDeps	Don't normalise over these parameters when calculating the sWeights. Will be passed on to AddSWeight().
[in]	useWeights	Include weights of the input data in calculation of s weights.
[in]	cloneData	Make a clone of the incoming data before adding weights.
[in]	newName	New name for the data.
[in]	argX	Additional arguments for the fitting step in AddSWeight().

Definition at line 198 of file SPlot.cxx.

Member Function Documentation

AddSWeight()

void SPlot::AddSWeight	(	RooAbsPdf *	pdf,
		const RooArgList &	yieldsTmp,
		const RooArgSet &	projDeps = RooArgSet(),
		bool	includeWeights = kTRUE,
		const RooCmdArg &	arg5 = RooCmdArg::none(),
		const RooCmdArg &	arg6 = RooCmdArg::none(),
		const RooCmdArg &	arg7 = RooCmdArg::none(),
		const RooCmdArg &	arg8 = RooCmdArg::none()
	)

Method which adds the sWeights to the dataset.

The SPlot will contain two new variables for each yield parameter:

• L_<varname> is the the likelihood for each event, i.e., the pdf evaluated for the a given value of the variable "varname".
• <varname>_sw is the value of the sWeight for the variable "varname" for each event.

Find Parameters in the PDF to be considered fixed when calculating the SWeights and be sure to NOT include the yields in that list.

After fixing non-yield parameters, this function will start a fit by calling

pdf->fitTo(*fSData, RooFit::Extended(kTRUE), RooFit::SumW2Error(kTRUE), RooFit::PrintLevel(-1), RooFit::PrintEvalErrors(-1)).

One can pass additional arguments to fitTo, such as RooFit::Range("fitrange"), as arg5, arg6, arg7, arg8.

Note

A RooFit::Range may be necessary to get expected results if you initially fit in a range and/or called pdf->fixCoefRange("fitrange") on pdf. Pass arg5, arg6, arg7, arg8 AT YOUR OWN RISK.

Parameters

[in]	pdf	PDF to fit to data to compute s weights.
[in]	yieldsTmp	Yields to use to compute s weights.
[in]	projDeps	These will not be normalized over when calculating the sWeights, and will be considered parameters, not observables.
[in]	includeWeights	Include weights of the input data in calculation of s weights.
[in]	argX	Optional additional arguments for the fitting step.

Definition at line 419 of file SPlot.cxx.

GetNumSWeightVars()

Int_t SPlot::GetNumSWeightVars

(

)

const

Return the number of SWeights In other words, return the number of species that we are trying to extract.

Definition at line 386 of file SPlot.cxx.

GetSDataSet()

RooDataSet * SPlot::GetSDataSet

(

)

const

Retrieve s-weighted data.

It does not automatically call AddSWeight(). This needs to be done manually.

Definition at line 242 of file SPlot.cxx.

GetSumOfEventSWeight()

Double_t SPlot::GetSumOfEventSWeight

(

Int_t

numEvent

)

const

Sum the SWeights for a particular event.

This sum should equal the total weight of that event. This method is intended to be used as a check.

Definition at line 300 of file SPlot.cxx.

GetSWeight()

Double_t SPlot::GetSWeight	(	Int_t	numEvent,
		const char *	sVariable
	)		const

Retrieve an s weight.

Parameters

[in]	numEvent	Event number to retrieve s weight for.
[in]	sVariable	The yield parameter to retrieve the s weight for.

Definition at line 251 of file SPlot.cxx.

GetSWeightVars()

RooArgList SPlot::GetSWeightVars

(

)

const

Return a RooArgList containing all paramters that have s weights.

Definition at line 372 of file SPlot.cxx.

GetYieldFromSWeight()

Double_t SPlot::GetYieldFromSWeight

(

const char *

sVariable

)

const

Sum the SWeights for a particular species over all events.

This should equal the total (weighted) yield of that species. This method is intended as a check.

Definition at line 331 of file SPlot.cxx.

SetSData()

RooDataSet * SPlot::SetSData

(

RooDataSet *

data

)

Set dataset (if not passed in constructor).

Definition at line 230 of file SPlot.cxx.

Member Data Documentation

fSData

RooDataSet* RooStats::SPlot::fSData

protected

Definition at line 82 of file SPlot.h.

fSWeightVars

RooArgList RooStats::SPlot::fSWeightVars

protected

Definition at line 78 of file SPlot.h.

Libraries for RooStats::SPlot:

---

The documentation for this class was generated from the following files:

• roofit/roostats/inc/RooStats/SPlot.h
• roofit/roostats/src/SPlot.cxx