Class that helps perform filtering (Butterworth, Davison, Rubin and Salam, arXiv:0802.2470) and trimming (Krohn, Thaler and Wang, arXiv:0912.1342) on jets, optionally in conjunction with subtraction (Cacciari and Salam, arXiv:0707.1378). More...

#include <fastjet/tools/Filter.hh>

Inheritance diagram for fastjet::Filter:

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Collaboration diagram for fastjet::Filter:

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Public Types
typedef FilterStructure	StructureType

Public Types inherited from fastjet::Transformer
typedef PseudoJetStructureBase	StructureType
	A typedef that is needed to ensure that the PseudoJet::structure_of() template function works.

Public Member Functions
	Filter ()
	trivial ctor Note: this is just for derived classes a Filter initialised through this constructor will not work!

	Filter (JetDefinition subjet_def, Selector selector, double rho=0.0)
	define a filter that decomposes a jet into subjets using a generic JetDefinition and then keeps only a subset of these subjets according to a Selector. More...

	Filter (double Rfilt, Selector selector, double rho=0.0)
	Same as the full constructor (see above) but just specifying the radius By default, Cambridge-Aachen is used If the jet (or all its pieces) is obtained with a non-default recombiner, that one will be used. More...

	Filter (FunctionOfPseudoJet< double > *Rfilt_func, Selector selector, double rho=0.0)
	Same as the full constructor (see above) but just specifying a filtering radius that will depend on the jet being filtered As for the previous case, Cambridge-Aachen is used If the jet (or all its pieces) is obtained with a non-default recombiner, that one will be used. More...

virtual	~Filter ()
	default dtor

void	set_subtractor (const FunctionOfPseudoJet< PseudoJet > *subtractor)
	Set a subtractor that is applied to all individual subjets before deciding which ones to keep. More...

virtual PseudoJet	result (const PseudoJet &jet) const
	runs the filtering and sets kept and rejected to be the jets of interest (with non-zero rho, they will have been subtracted). More...

virtual std::string	description () const
	class description

Public Member Functions inherited from fastjet::Transformer
	Transformer ()
	default ctor

virtual	~Transformer ()
	default dtor

Public Member Functions inherited from fastjet::FunctionOfPseudoJet< PseudoJet >
	FunctionOfPseudoJet ()
	default ctor

virtual	~FunctionOfPseudoJet ()
	default dtor (virtual to allow safe polymorphism)

PseudoJet	operator() (const PseudoJet &pj) const
	apply the function using the "traditional" () operator. More...

std::vector< PseudoJet >	operator() (const std::vector< PseudoJet > &pjs) const
	apply the function on a vector of PseudoJet, returning a vector of the results. More...

Detailed Description

Class that helps perform filtering (Butterworth, Davison, Rubin and Salam, arXiv:0802.2470) and trimming (Krohn, Thaler and Wang, arXiv:0912.1342) on jets, optionally in conjunction with subtraction (Cacciari and Salam, arXiv:0707.1378).

For example, to apply filtering that reclusters a jet's constituents with the Cambridge/Aachen jet algorithm with R=0.3 and then selects the 3 hardest subjets, one can use the following code:

Filter filter(JetDefinition(cambridge_algorithm, 0.3), SelectorNHardest(3));

PseudoJet filtered_jet = filter(original_jet);

To obtain trimming, involving for example the selection of all subjets carrying at least 3% of the original jet's pt, the selector would be replaced by SelectorPtFractionMin(0.03).

To additionally perform subtraction on the subjets prior to selection, either include a 3rd argument specifying the background density rho, or call the set_subtractor(...) member function. If subtraction is requested, the original jet must be the result of a clustering with active area with explicit ghosts support or a merging of such pieces.

The information on the subjets that were kept and rejected can be obtained using:

vector<PseudoJet> kept_subjets = filtered_jet.pieces();

vector<PseudoJet> rejected_subjets = filtered_jet.structure_of<Filter>().rejected();

Implementation Note

If the original jet was defined with the Cambridge/Aachen algorithm (or is made of pieces each of which comes from the C/A alg) and the filtering definition is C/A, then the filter does not rerun the C/A algorithm on the constituents, but instead makes use of the existent C/A cluster sequence in the original jet. This increases the speed of the filter.

See also 11 - use of filtering for a further usage example.

Support for areas, reuse of C/A cluster sequences, etc., considerably complicates the implementation of Filter. For an explanation of how a simpler filter might be coded, see the "User-defined transformers" appendix of the manual.

Definition at line 97 of file Filter.hh.

Constructor & Destructor Documentation

fastjet::Filter::Filter	(	JetDefinition	subjet_def,
		Selector	selector,
		double	rho = `0.0`
	)

inline

define a filter that decomposes a jet into subjets using a generic JetDefinition and then keeps only a subset of these subjets according to a Selector.

Optionally, each subjet may be internally bakground-subtracted prior to selection.

Parameters

subjet_def	the jet definition applied to obtain the subjets
selector	the Selector applied to compute the kept subjets
rho	if non-zero, backgruond-subtract each subjet befor selection

Note: internal subtraction only applies on jets that are obtained with a cluster sequence with area support and explicit ghosts

Definition at line 116 of file Filter.hh.

fastjet::Filter::Filter	(	double	Rfilt,
		Selector	selector,
		double	rho = `0.0`
	)

inline

Same as the full constructor (see above) but just specifying the radius By default, Cambridge-Aachen is used If the jet (or all its pieces) is obtained with a non-default recombiner, that one will be used.

Parameters

Rfilt the filtering radius

Definition at line 124 of file Filter.hh.

fastjet::Filter::Filter	(	FunctionOfPseudoJet< double > *	Rfilt_func,
		Selector	selector,
		double	rho = `0.0`
	)

inline

Same as the full constructor (see above) but just specifying a filtering radius that will depend on the jet being filtered As for the previous case, Cambridge-Aachen is used If the jet (or all its pieces) is obtained with a non-default recombiner, that one will be used.

Parameters

Rfilt_func the filtering radius function of a PseudoJet

Definition at line 136 of file Filter.hh.

Member Function Documentation

void fastjet::Filter::set_subtractor ( const FunctionOfPseudoJet< PseudoJet > * subtractor )

inline

Set a subtractor that is applied to all individual subjets before deciding which ones to keep.

It takes precedence over a non-zero rho.

Definition at line 144 of file Filter.hh.

PseudoJet fastjet::Filter::result ( const PseudoJet & jet ) const

virtual

runs the filtering and sets kept and rejected to be the jets of interest (with non-zero rho, they will have been subtracted).

Parameters

jet	the jet that gets filtered

Returns: the filtered jet

Implements fastjet::Transformer.

Definition at line 81 of file Filter.cc.

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

tools/fastjet/tools/Filter.hh
tools/Filter.cc

Public Types

Public Member Functions

Detailed Description

Implementation Note

Constructor & Destructor Documentation

Member Function Documentation