Class to estimate the pt density of the background per unit area, using the median of the distribution of pt/area from jets that pass some selection criterion. More...

#include <fastjet/tools/JetMedianBackgroundEstimator.hh>

Inheritance diagram for fastjet::JetMedianBackgroundEstimator:

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Collaboration diagram for fastjet::JetMedianBackgroundEstimator:

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Public Member Functions
constructors and destructors
	JetMedianBackgroundEstimator (const Selector &rho_range, const JetDefinition &jet_def, const AreaDefinition &area_def)
	Constructor that sets the rho range as well as the jet definition and area definition to be used to cluster the particles. More...

	JetMedianBackgroundEstimator (const Selector &rho_range, const ClusterSequenceAreaBase &csa)
	ctor from a ClusterSequenceAreaBase with area More...

	JetMedianBackgroundEstimator (const Selector &rho_range=SelectorIdentity())
	Default constructor that optionally sets the rho range. More...

	~JetMedianBackgroundEstimator ()
	default dtor

setting a new event
virtual void	set_particles (const std::vector< PseudoJet > &particles)
	tell the background estimator that it has a new event, composed of the specified particles. More...

void	set_cluster_sequence (const ClusterSequenceAreaBase &csa)
	(re)set the cluster sequence (with area support) to be used by future calls to rho() etc. More...

void	set_jets (const std::vector< PseudoJet > &jets)
	(re)set the jets (which must have area support) to be used by future calls to rho() etc. More...

void	set_selector (const Selector &rho_range_selector)
	(re)set the selector to be used for future calls to rho() etc.

void	set_compute_rho_m (bool enable)
	determine whether the automatic calculation of rho_m and sigma_m is enabled (by default true)

retrieving fundamental information
double	rho () const
	get rho, the median background density per unit area

double	sigma () const
	get sigma, the background fluctuations per unit area

double	rho (const PseudoJet &jet)
	get rho, the median background density per unit area, locally at the position of a given jet. More...

double	sigma (const PseudoJet &jet)
	get sigma, the background fluctuations per unit area, locally at the position of a given jet. More...

virtual bool	has_sigma ()
	returns true if this background estimator has support for determination of sigma

virtual double	rho_m () const
	returns rho_m, the purely longitudinal, particle-mass-induced component of the background density per unit area

virtual double	sigma_m () const
	returns sigma_m, a measure of the fluctuations in the purely longitudinal, particle-mass-induced component of the background density per unit area; must be multipled by sqrt(area) to get fluctuations for a region of a given area. More...

virtual double	rho_m (const PseudoJet &)
	Returns rho_m locally at the jet position. As for rho(jet), it is non-const.

virtual double	sigma_m (const PseudoJet &)
	Returns sigma_m locally at the jet position. As for rho(jet), it is non-const.

virtual bool	has_rho_m () const
	Returns true if this background estimator has support for determination of rho_m. More...

retrieving additional useful information
double	mean_area () const
	Returns the mean area of the jets used to actually compute the background properties in the last call of rho() or sigma() If the configuration has changed in the meantime, throw an error. More...

unsigned int	n_jets_used () const
	returns the number of jets used to actually compute the background properties in the last call of rho() or sigma() If the configuration has changed in the meantime, throw an error. More...

std::vector< PseudoJet >	jets_used () const
	returns the jets used to actually compute the background properties

double	empty_area () const
	Returns the estimate of the area (within the range defined by the selector) that is not occupied by jets. More...

double	n_empty_jets () const
	Returns the number of empty jets used when computing the background properties. More...

configuring behaviour
void	reset ()
	Resets the class to its default state, including the choice to use 4-vector areas.

void	set_use_area_4vector (bool use_it=true)
	By default when calculating pt/Area for a jet, it is the transverse component of the 4-vector area that is used in the ratiof . More...

bool	use_area_4vector () const
	check if the estimator uses the 4-vector area or the scalar area

void	set_provide_fj2_sigma (bool provide_fj2_sigma=true)
	The FastJet v2.X sigma calculation had a small spurious offset in the limit of a small number of jets. More...

void	set_jet_density_class (const FunctionOfPseudoJet< double > *jet_density_class)
	Set a pointer to a class that calculates the quantity whose median will be calculated; if the pointer is null then pt/area is used (as occurs also if this function is not called). More...

const FunctionOfPseudoJet < double > *	jet_density_class () const
	return the pointer to the jet density class

virtual void	set_rescaling_class (const FunctionOfPseudoJet< double > *rescaling_class_in)
	Set a pointer to a class that calculates the rescaling factor as a function of the jet (position). More...

description
std::string	description () const
	returns a textual description of the background estimator

Public Member Functions inherited from fastjet::BackgroundEstimatorBase
virtual	~BackgroundEstimatorBase ()
	a default virtual destructor that does nothing

	BackgroundEstimatorBase ()

const FunctionOfPseudoJet < double > *	rescaling_class () const
	return the pointer to the jet density class

Additional Inherited Members
Protected Member Functions inherited from fastjet::BackgroundEstimatorBase
void	_median_and_stddev (const std::vector< double > &quantity_vector, double n_empty_jets, double &median, double &stand_dev_if_gaussian, bool do_fj2_calculation=false) const
	given a quantity in a vector (e.g. More...

double	_percentile (const std::vector< double > &sorted_quantity_vector, const double percentile, const double nempty=0.0, const bool do_fj2_calculation=false) const
	computes a percentile of a given sorted vector More...

Protected Attributes inherited from fastjet::BackgroundEstimatorBase
const FunctionOfPseudoJet < double > *	_rescaling_class

Static Protected Attributes inherited from fastjet::BackgroundEstimatorBase
static LimitedWarning	_warnings_empty_area

Detailed Description

Class to estimate the pt density of the background per unit area, using the median of the distribution of pt/area from jets that pass some selection criterion.

Events are passed either in the form of the event particles (in which they're clustered by the class), a ClusterSequenceArea (in which case the jets used are those returned by "inclusive_jets()") or directly as a set of jets.

The selection criterion is typically a geometrical one (e.g. all jets with |y|<2) sometimes supplemented with some kinematical restriction (e.g. exclusion of the two hardest jets). It is passed to the class through a Selector.

Beware: by default, to correctly handle partially empty events, the class attempts to calculate an "empty area", based (schematically) on

   range.total_area() - sum_{jets_in_range} jets.area()

For ranges with small areas, this can be inaccurate (particularly relevant in dense events where empty_area should be zero and ends up not being zero).

This calculation of empty area can be avoided if a ClusterSequenceArea class with explicit ghosts (ActiveAreaExplicitGhosts) is used. This is recommended unless speed requirements cause you to use Voronoi areas. For speedy background estimation you could also consider using GridMedianBackgroundEstimator.

Definition at line 80 of file JetMedianBackgroundEstimator.hh.

Constructor & Destructor Documentation

fastjet::JetMedianBackgroundEstimator::JetMedianBackgroundEstimator	(	const Selector &	rho_range,
		const JetDefinition &	jet_def,
		const AreaDefinition &	area_def
	)

Constructor that sets the rho range as well as the jet definition and area definition to be used to cluster the particles.

Prior to the estimation of rho, one has to provide the particles to cluster using set_particles(...)

Parameters

rho_range	the Selector specifying which jets will be considered
jet_def	the jet definition to use for the clustering
area_def	the area definition to use for the clustering

Definition at line 84 of file JetMedianBackgroundEstimator.cc.

fastjet::JetMedianBackgroundEstimator::JetMedianBackgroundEstimator	(	const Selector &	rho_range,
		const ClusterSequenceAreaBase &	csa
	)

ctor from a ClusterSequenceAreaBase with area

Parameters

rho_range	the Selector specifying which jets will be considered
csa	the ClusterSequenceArea to use

Pre-conditions:

one should be able to estimate the "empty area" (i.e. the area not occupied by jets). This is feasible if at least one of the following conditions is satisfied: ( i) the ClusterSequence has explicit ghosts (ii) the range has a computable area.
the jet algorithm must be suited for median computation (otherwise a warning will be issues)

Note that selectors with e.g. hardest-jets exclusion do not have a well-defined area. For this reasons, it is STRONGLY advised to use an area with explicit ghosts.

Definition at line 101 of file JetMedianBackgroundEstimator.cc.

fastjet::JetMedianBackgroundEstimator::JetMedianBackgroundEstimator ( const Selector & rho_range = SelectorIdentity() )

inline

Default constructor that optionally sets the rho range.

The configuration must be done later calling set_cluster_sequence(...) or set_jets(...).

Parameters

rho_range the Selector specifying which jets will be considered

Definition at line 124 of file JetMedianBackgroundEstimator.hh.

Member Function Documentation

void fastjet::JetMedianBackgroundEstimator::set_particles ( const std::vector< PseudoJet > & particles )

virtual

tell the background estimator that it has a new event, composed of the specified particles.

Implements fastjet::BackgroundEstimatorBase.

Definition at line 117 of file JetMedianBackgroundEstimator.cc.

void fastjet::JetMedianBackgroundEstimator::set_cluster_sequence ( const ClusterSequenceAreaBase & csa )

(re)set the cluster sequence (with area support) to be used by future calls to rho() etc.

Parameters

csa	the cluster sequence area

Pre-conditions:

one should be able to estimate the "empty area" (i.e. the area not occupied by jets). This is feasible if at least one of the following conditions is satisfied: ( i) the ClusterSequence has explicit ghosts (ii) the range selected has a computable area.
the jet algorithm must be suited for median computation (otherwise a warning will be issues)

Note that selectors with e.g. hardest-jets exclusion do not have a well-defined area. For this reasons, it is STRONGLY advised to use an area with explicit ghosts.

Definition at line 160 of file JetMedianBackgroundEstimator.cc.

void fastjet::JetMedianBackgroundEstimator::set_jets ( const std::vector< PseudoJet > & jets )

(re)set the jets (which must have area support) to be used by future calls to rho() etc.

; for the conditions that must be satisfied by the jets, see the Constructor that takes jets.

Definition at line 184 of file JetMedianBackgroundEstimator.cc.

double fastjet::JetMedianBackgroundEstimator::rho ( const PseudoJet & jet )

virtual

get rho, the median background density per unit area, locally at the position of a given jet.

If the Selector associated with the range takes a reference jet (i.e. is relocatable), then for subsequent operations the Selector has that jet set as its reference.

Implements fastjet::BackgroundEstimatorBase.

Definition at line 250 of file JetMedianBackgroundEstimator.cc.

double fastjet::JetMedianBackgroundEstimator::sigma ( const PseudoJet & jet )

virtual

get sigma, the background fluctuations per unit area, locally at the position of a given jet.

If the Selector associated with the range takes a reference jet (i.e. is relocatable), then for subsequent operations the Selector has that jet set as its reference.

Reimplemented from fastjet::BackgroundEstimatorBase.

Definition at line 265 of file JetMedianBackgroundEstimator.cc.

double fastjet::JetMedianBackgroundEstimator::sigma_m ( ) const

virtual

returns sigma_m, a measure of the fluctuations in the purely longitudinal, particle-mass-induced component of the background density per unit area; must be multipled by sqrt(area) to get fluctuations for a region of a given area.

Reimplemented from fastjet::BackgroundEstimatorBase.

Definition at line 292 of file JetMedianBackgroundEstimator.cc.

virtual bool fastjet::JetMedianBackgroundEstimator::has_rho_m ( ) const

inlinevirtual

Returns true if this background estimator has support for determination of rho_m.

In te presence of a density class, support for rho_m is automatically disabled

Note that support for sigma_m is automatic is one has sigma and rho_m support.

Reimplemented from fastjet::BackgroundEstimatorBase.

Definition at line 237 of file JetMedianBackgroundEstimator.hh.

double fastjet::JetMedianBackgroundEstimator::mean_area ( ) const

inline

Returns the mean area of the jets used to actually compute the background properties in the last call of rho() or sigma() If the configuration has changed in the meantime, throw an error.

Definition at line 246 of file JetMedianBackgroundEstimator.hh.

unsigned int fastjet::JetMedianBackgroundEstimator::n_jets_used ( ) const

inline

returns the number of jets used to actually compute the background properties in the last call of rho() or sigma() If the configuration has changed in the meantime, throw an error.

Definition at line 256 of file JetMedianBackgroundEstimator.hh.

double fastjet::JetMedianBackgroundEstimator::empty_area ( ) const

inline

Returns the estimate of the area (within the range defined by the selector) that is not occupied by jets.

The value is that for the last call of rho() or sigma() If the configuration has changed in the meantime, throw an error.

The answer is defined to be zero if the area calculation involved explicit ghosts; if the area calculation was an active area, then use is made of the active area's internal list of pure ghost jets (taking those that pass the selector); otherwise it is based on the difference between the selector's total area and the area of the jets that pass the selector.

The result here is just the cached result of the corresponding call to the ClusterSequenceAreaBase function.

Definition at line 290 of file JetMedianBackgroundEstimator.hh.

double fastjet::JetMedianBackgroundEstimator::n_empty_jets ( ) const

inline

Returns the number of empty jets used when computing the background properties.

The value is that for the last call of rho() or sigma(). If the configuration has changed in the meantime, throw an error.

If the area has explicit ghosts the result is zero; for active areas it is the number of internal pure ghost jets that pass the selector; otherwise it is deduced from the empty area, divided by $0.55 \pi R^2$ (the average pure-ghost-jet area).

The result here is just the cached result of the corresponding call to the ClusterSequenceAreaBase function.

Definition at line 309 of file JetMedianBackgroundEstimator.hh.

void fastjet::JetMedianBackgroundEstimator::set_use_area_4vector ( bool use_it = true )

inline

By default when calculating pt/Area for a jet, it is the transverse component of the 4-vector area that is used in the ratiof $p_t/A$ .

Calling this function with a "false" argument causes the scalar area to be used instead.

While the difference between the two choices is usually small, for high-precision work it is usually the 4-vector area that is to be preferred.

Parameters

use_it whether one uses the 4-vector area or not (true by default)

Definition at line 338 of file JetMedianBackgroundEstimator.hh.

void fastjet::JetMedianBackgroundEstimator::set_provide_fj2_sigma ( bool provide_fj2_sigma = true )

inline

The FastJet v2.X sigma calculation had a small spurious offset in the limit of a small number of jets.

This is fixed by default in versions 3 upwards. The old behaviour can be obtained with a call to this function.

Definition at line 350 of file JetMedianBackgroundEstimator.hh.

void fastjet::JetMedianBackgroundEstimator::set_jet_density_class ( const FunctionOfPseudoJet< double > * jet_density_class )

Set a pointer to a class that calculates the quantity whose median will be calculated; if the pointer is null then pt/area is used (as occurs also if this function is not called).

Note that this is still preliminary in FastJet 3.0 and that backward compatibility is not guaranteed in future releases of FastJet

Definition at line 358 of file JetMedianBackgroundEstimator.cc.

virtual void fastjet::JetMedianBackgroundEstimator::set_rescaling_class ( const FunctionOfPseudoJet< double > * rescaling_class_in )

inlinevirtual

Set a pointer to a class that calculates the rescaling factor as a function of the jet (position).

Note that the rescaling factor is used both in the determination of the "global" rho (the pt/A of each jet is divided by this factor) and when asking for a local rho (the result is multiplied by this factor).

The BackgroundRescalingYPolynomial class can be used to get a rescaling that depends just on rapidity.

Reimplemented from fastjet::BackgroundEstimatorBase.

Definition at line 377 of file JetMedianBackgroundEstimator.hh.

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

tools/fastjet/tools/JetMedianBackgroundEstimator.hh
tools/JetMedianBackgroundEstimator.cc

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation