FastJet  3.0.6
JetMedianBackgroundEstimator.hh
1 #ifndef __FASTJET_BACKGROUND_ESTIMATOR_HH__
2 #define __FASTJET_BACKGROUND_ESTIMATOR_HH__
3 
4 //STARTHEADER
5 // $Id: JetMedianBackgroundEstimator.hh 2689 2011-11-14 14:51:06Z soyez $
6 //
7 // Copyright (c) 2005-2011, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
8 //
9 //----------------------------------------------------------------------
10 // This file is part of FastJet.
11 //
12 // FastJet is free software; you can redistribute it and/or modify
13 // it under the terms of the GNU General Public License as published by
14 // the Free Software Foundation; either version 2 of the License, or
15 // (at your option) any later version.
16 //
17 // The algorithms that underlie FastJet have required considerable
18 // development and are described in hep-ph/0512210. If you use
19 // FastJet as part of work towards a scientific publication, please
20 // include a citation to the FastJet paper.
21 //
22 // FastJet is distributed in the hope that it will be useful,
23 // but WITHOUT ANY WARRANTY; without even the implied warranty of
24 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
25 // GNU General Public License for more details.
26 //
27 // You should have received a copy of the GNU General Public License
28 // along with FastJet. If not, see <http://www.gnu.org/licenses/>.
29 //----------------------------------------------------------------------
30 //ENDHEADER
31 
32 #include <fastjet/ClusterSequenceAreaBase.hh>
33 #include <fastjet/AreaDefinition.hh>
34 #include <fastjet/FunctionOfPseudoJet.hh>
35 #include <fastjet/Selector.hh>
36 #include <fastjet/tools/BackgroundEstimatorBase.hh>
37 #include <iostream>
38 
39 FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
40 
41 
42 /// @ingroup tools_background
43 /// \class JetMedianBackgroundEstimator
44 ///
45 /// Class to estimate the pt density of the background per unit area,
46 /// using the median of the distribution of pt/area from jets that
47 /// pass some selection criterion.
48 ///
49 /// Events are passed either in the form of the event particles (in
50 /// which they're clustered by the class), a ClusterSequenceArea (in
51 /// which case the jets used are those returned by "inclusive_jets()")
52 /// or directly as a set of jets.
53 ///
54 /// The selection criterion is typically a geometrical one (e.g. all
55 /// jets with |y|<2) sometimes supplemented with some kinematical
56 /// restriction (e.g. exclusion of the two hardest jets). It is passed
57 /// to the class through a Selector.
58 ///
59 /// Beware:
60 /// by default, to correctly handle partially empty events, the
61 /// class attempts to calculate an "empty area", based
62 /// (schematically) on
63 ///
64 /// range.total_area() - sum_{jets_in_range} jets.area()
65 ///
66 /// For ranges with small areas, this can be inaccurate (particularly
67 /// relevant in dense events where empty_area should be zero and ends
68 /// up not being zero).
69 ///
70 /// This calculation of empty area can be avoided if a
71 /// ClusterSequenceArea class with explicit ghosts
72 /// (ActiveAreaExplicitGhosts) is used. This is _recommended_
73 /// unless speed requirements cause you to use Voronoi areas. For
74 /// speedy background estimation you could also consider using
75 /// GridMedianBackgroundEstimator.
76 ///
77 ///
79 public:
80  /// @name constructors and destructors
81  //\{
82  //----------------------------------------------------------------
83  /// Constructor that sets the rho range as well as the jet
84  /// definition and area definition to be used to cluster the
85  /// particles. Prior to the estimation of rho, one has to provide
86  /// the particles to cluster using set_particles(...)
87  ///
88  /// \param rho_range the Selector specifying which jets will be considered
89  /// \param jet_def the jet definition to use for the clustering
90  /// \param area_def the area definition to use for the clustering
91  JetMedianBackgroundEstimator(const Selector &rho_range,
92  const JetDefinition &jet_def,
93  const AreaDefinition &area_def);
94 
95  /// ctor from a ClusterSequenceAreaBase with area
96  ///
97  /// \param rho_range the Selector specifying which jets will be considered
98  /// \param csa the ClusterSequenceArea to use
99  ///
100  /// Pre-conditions:
101  /// - one should be able to estimate the "empty area" (i.e. the area
102  /// not occupied by jets). This is feasible if at least one of the following
103  /// conditions is satisfied:
104  /// ( i) the ClusterSequence has explicit ghosts
105  /// (ii) the range has a computable area.
106  /// - the jet algorithm must be suited for median computation
107  /// (otherwise a warning will be issues)
108  ///
109  /// Note that selectors with e.g. hardest-jets exclusion do not have
110  /// a well-defined area. For this reasons, it is STRONGLY advised to
111  /// use an area with explicit ghosts.
112  JetMedianBackgroundEstimator(const Selector &rho_range,
113  const ClusterSequenceAreaBase &csa);
114 
115 
116  /// Default constructor that optionally sets the rho range. The
117  /// configuration must be done later calling
118  /// set_cluster_sequence(...) or set_jets(...).
119  ///
120  /// \param rho_range the Selector specifying which jets will be considered
121  ///
122  JetMedianBackgroundEstimator(const Selector &rho_range = SelectorIdentity())
123  : _rho_range(rho_range), _jet_def(JetDefinition()) { reset(); }
124 
125 
126  /// default dtor
128 
129  //\}
130 
131 
132  /// @name setting a new event
133  //\{
134  //----------------------------------------------------------------
135 
136  /// tell the background estimator that it has a new event, composed
137  /// of the specified particles.
138  virtual void set_particles(const std::vector<PseudoJet> & particles);
139 
140  /// (re)set the cluster sequence (with area support) to be used by
141  /// future calls to rho() etc.
142  ///
143  /// \param csa the cluster sequence area
144  ///
145  /// Pre-conditions:
146  /// - one should be able to estimate the "empty area" (i.e. the area
147  /// not occupied by jets). This is feasible if at least one of the following
148  /// conditions is satisfied:
149  /// ( i) the ClusterSequence has explicit ghosts
150  /// (ii) the range selected has a computable area.
151  /// - the jet algorithm must be suited for median computation
152  /// (otherwise a warning will be issues)
153  ///
154  /// Note that selectors with e.g. hardest-jets exclusion do not have
155  /// a well-defined area. For this reasons, it is STRONGLY advised to
156  /// use an area with explicit ghosts.
157  void set_cluster_sequence(const ClusterSequenceAreaBase & csa);
158 
159  /// (re)set the jets (which must have area support) to be used by future
160  /// calls to rho() etc.; for the conditions that must be satisfied
161  /// by the jets, see the Constructor that takes jets.
162  void set_jets(const std::vector<PseudoJet> &jets);
163 
164  /// (re)set the selector to be used for future calls to rho() etc.
165  void set_selector(const Selector & rho_range_selector) {
166  _rho_range = rho_range_selector;
167  _uptodate = false;
168  }
169 
170  //\}
171 
172 
173  /// @name retrieving fundamental information
174  //\{
175  //----------------------------------------------------------------
176 
177  /// get rho, the median background density per unit area
178  double rho() const;
179 
180  /// get sigma, the background fluctuations per unit area
181  double sigma() const;
182 
183  /// get rho, the median background density per unit area, locally at
184  /// the position of a given jet.
185  ///
186  /// If the Selector associated with the range takes a reference jet
187  /// (i.e. is relocatable), then for subsequent operations the
188  /// Selector has that jet set as its reference.
189  double rho(const PseudoJet & jet);
190 
191  /// get sigma, the background fluctuations per unit area,
192  /// locally at the position of a given jet.
193  ///
194  /// If the Selector associated with the range takes a reference jet
195  /// (i.e. is relocatable), then for subsequent operations the
196  /// Selector has that jet set as its reference.
197  double sigma(const PseudoJet &jet);
198 
199  /// returns true if this background estimator has support for
200  /// determination of sigma
201  virtual bool has_sigma() {return true;}
202 
203  //\}
204 
205  /// @name retrieving additional useful information
206  //\{
207  //----------------------------------------------------------------
208  /// Returns the mean area of the jets used to actually compute the
209  /// background properties in the last call of rho() or sigma()
210  double mean_area() const{
211  _recompute_if_needed();
212  return _mean_area;
213  }
214 
215  /// returns the number of jets used to actually compute the
216  /// background properties in the last call of rho() or sigma()
217  unsigned int n_jets_used() const{
218  _recompute_if_needed();
219  return _n_jets_used;
220  }
221 
222  /// Returns the estimate of the area (within the range defined by
223  /// the selector) that is not occupied by jets. The value is that
224  /// for the last call of rho() or sigma()
225  ///
226  /// The answer is defined to be zero if the area calculation
227  /// involved explicit ghosts; if the area calculation was an active
228  /// area, then use is made of the active area's internal list of
229  /// pure ghost jets (taking those that pass the selector); otherwise
230  /// it is based on the difference between the selector's total area
231  /// and the area of the jets that pass the selector.
232  ///
233  /// The result here is just the cached result of the corresponding
234  /// call to the ClusterSequenceAreaBase function.
235  double empty_area() const{
236  _recompute_if_needed();
237  return _empty_area;
238  }
239 
240  /// Returns the number of empty jets used when computing the
241  /// background properties. The value is that for the last call of
242  /// rho() or sigma().
243  ///
244  /// If the area has explicit ghosts the result is zero; for active
245  /// areas it is the number of internal pure ghost jets that pass the
246  /// selector; otherwise it is deduced from the empty area, divided by
247  /// \f$ 0.55 \pi R^2 \f$ (the average pure-ghost-jet area).
248  ///
249  /// The result here is just the cached result of the corresponding
250  /// call to the ClusterSequenceAreaBase function.
251  double n_empty_jets() const{
252  _recompute_if_needed();
253  return _n_empty_jets;
254  }
255 
256  //}
257 
258 
259  /// @name configuring behaviour
260  //\{
261  //----------------------------------------------------------------
262 
263  /// Resets the class to its default state, including the choice to
264  /// use 4-vector areas.
265  ///
266  void reset();
267 
268  /// By default when calculating pt/Area for a jet, it is the
269  /// transverse component of the 4-vector area that is used in the ratiof \f$p_t/A\f$.
270  /// Calling this function with a "false" argument causes the scalar area to
271  /// be used instead.
272  ///
273  /// While the difference between the two choices is usually small,
274  /// for high-precision work it is usually the 4-vector area that is
275  /// to be preferred.
276  ///
277  /// \param use_it whether one uses the 4-vector area or not (true by default)
278  void set_use_area_4vector(bool use_it = true){
279  _use_area_4vector = use_it;
280  _uptodate = false;
281  }
282 
283  /// check if the estimator uses the 4-vector area or the scalar area
284  bool use_area_4vector() const{ return _use_area_4vector;}
285 
286  /// The FastJet v2.X sigma calculation had a small spurious offset
287  /// in the limit of a small number of jets. This is fixed by default
288  /// in versions 3 upwards. The old behaviour can be obtained with a
289  /// call to this function.
290  void set_provide_fj2_sigma(bool provide_fj2_sigma = true) {
291  _provide_fj2_sigma = provide_fj2_sigma;
292  _uptodate = false;
293  }
294 
295  /// Set a pointer to a class that calculates the quantity whose
296  /// median will be calculated; if the pointer is null then pt/area
297  /// is used (as occurs also if this function is not called).
298  ///
299  /// Note that this is still <i>preliminary</i> in FastJet 3.0 and
300  /// that backward compatibility is not guaranteed in future releases
301  /// of FastJet
302  void set_jet_density_class(const FunctionOfPseudoJet<double> * jet_density_class);
303 
304  /// return the pointer to the jet density class
306  return _jet_density_class;
307  }
308 
309  /// Set a pointer to a class that calculates the rescaling factor as
310  /// a function of the jet (position). Note that the rescaling factor
311  /// is used both in the determination of the "global" rho (the pt/A
312  /// of each jet is divided by this factor) and when asking for a
313  /// local rho (the result is multiplied by this factor).
314  ///
315  /// The BackgroundRescalingYPolynomial class can be used to get a
316  /// rescaling that depends just on rapidity.
317  virtual void set_rescaling_class(const FunctionOfPseudoJet<double> * rescaling_class_in) {
318  BackgroundEstimatorBase::set_rescaling_class(rescaling_class_in);
319  _uptodate = false;
320  }
321 
322  //\}
323 
324  /// @name description
325  //\{
326  //----------------------------------------------------------------
327 
328  /// returns a textual description of the background estimator
329  std::string description() const;
330 
331  //\}
332 
333 
334 private:
335 
336  /// do the actual job
337  void _compute() const;
338 
339  /// check if the properties need to be recomputed
340  /// and do so if needed
341  void _recompute_if_needed() const {
342  if (!_uptodate) _compute();
343  _uptodate = true;
344  }
345 
346  /// for estimation using a selector that takes a reference jet
347  /// (i.e. a selector that can be relocated) this function allows one
348  /// to set its position.
349  ///
350  /// Note that this HAS to be called before any attempt to compute
351  /// the background properties. The call is, however, performed
352  /// automatically by the functions rho(jet) and sigma(jet).
353  void _recompute_if_needed(const PseudoJet &jet);
354 
355  /// check that the underlying structure is still alive
356  /// throw an error otherwise
357  void _check_csa_alive() const;
358 
359  /// check that the algorithm used for the clustering is adapted for
360  /// background estimation (i.e. either kt or C/A)
361  /// Issue a warning otherwise
362  void _check_jet_alg_good_for_median() const;
363 
364  // the basic parameters of this class (passed through the variou ctors)
365  Selector _rho_range; ///< range to compute the background in
366  JetDefinition _jet_def; ///< the jet def to use for teh clustering
367  AreaDefinition _area_def; ///< the area def to use for teh clustering
368  std::vector<PseudoJet> _included_jets; ///< jets to be used
369 
370  // the tunable aprameters of the class
371  bool _use_area_4vector;
372  bool _provide_fj2_sigma;
373  const FunctionOfPseudoJet<double> * _jet_density_class;
374  //SharedPtr<BackgroundRescalingBase> _rescaling_class_sharedptr;
375 
376  // the actual results of the computation
377  mutable double _rho; ///< background estimated density per unit area
378  mutable double _sigma; ///< background estimated fluctuations
379  mutable double _mean_area; ///< mean area of the jets used to estimate the background
380  mutable unsigned int _n_jets_used; ///< number of jets used to estimate the background
381  mutable double _n_empty_jets; ///< number of empty (pure-ghost) jets
382  mutable double _empty_area; ///< the empty (pure-ghost/unclustered) area!
383 
384  // internal variables
385  SharedPtr<PseudoJetStructureBase> _csi; ///< allows to check if _csa is still valid
386  PseudoJet _current_reference; ///< current reference jet
387  mutable bool _uptodate; ///< true when the background computation is up-to-date
388 
389  /// handle warning messages
390  static LimitedWarning _warnings;
391  static LimitedWarning _warnings_zero_area;
392  static LimitedWarning _warnings_preliminary;
393 };
394 
395 
396 
397 
398 //----------------------------------------------------------------------
399 /// @ingroup tools_background
400 /// \class BackgroundJetPtDensity
401 /// Class that implements pt/area_4vector.perp() for background estimation
402 /// <i>(this is a preliminary class)</i>.
404 public:
405  virtual double result(const PseudoJet & jet) const {
406  return jet.perp() / jet.area_4vector().perp();
407  }
408  virtual std::string description() const {return "BackgroundJetPtDensity";}
409 };
410 
411 
412 //----------------------------------------------------------------------
413 /// @ingroup tools_background
414 /// \class BackgroundJetScalarPtDensity
415 /// Class that implements (scalar pt sum of jet)/(scalar area of jet)
416 /// for background estimation <i>(this is a preliminary class)</i>.
417 ///
418 /// Optionally it can return a quantity based on the sum of pt^n,
419 /// e.g. for use in subtracting fragementation function moments.
421 public:
422  /// Default constructor provides background estimation with scalar pt sum
423  BackgroundJetScalarPtDensity() : _pt_power(1) {}
424 
425  /// Constructor to provide background estimation based on
426  /// \f$ sum_{i\in jet} p_{ti}^{n} \f$
427  BackgroundJetScalarPtDensity(double n) : _pt_power(n) {}
428 
429  virtual double result(const PseudoJet & jet) const;
430 
431  virtual std::string description() const {return "BackgroundScalarJetPtDensity";}
432 
433 private:
434  double _pt_power;
435 };
436 
437 //----------------------------------------------------------------------
438 /// @ingroup tools_background
439 /// \class BackgroundJetPtMDensity
440 /// Class that implements
441 /// \f$ \frac{1}{A} \sum_{i \in jet} (\sqrt{p_{ti}^2+m^2} - p_{ti}) \f$
442 /// for background estimation <i>(this is a preliminary class)</i>.
443 ///
444 ///
445 /// This is useful for correcting jet masses in cases where the event
446 /// involves massive particles.
448 public:
449  virtual double result(const PseudoJet & jet) const {
450  std::vector<PseudoJet> constituents = jet.constituents();
451  double scalar_ptm = 0;
452  for (unsigned i = 0; i < constituents.size(); i++) {
453  scalar_ptm += constituents[i].mperp() - constituents[i].perp();
454  }
455  return scalar_ptm / jet.area();
456  }
457 
458  virtual std::string description() const {return "BackgroundPtMDensity";}
459 };
460 
461 
462 
463 FASTJET_END_NAMESPACE
464 
465 #endif // __BACKGROUND_ESTIMATOR_HH__
466 
fastjet::JetMedianBackgroundEstimator::~JetMedianBackgroundEstimator
~JetMedianBackgroundEstimator()
default dtor
Definition: JetMedianBackgroundEstimator.hh:127
fastjet::PseudoJet::area
virtual double area() const
return the jet (scalar) area.
Definition: PseudoJet.cc:703
fastjet::JetMedianBackgroundEstimator::mean_area
double mean_area() const
Returns the mean area of the jets used to actually compute the background properties in the last call...
Definition: JetMedianBackgroundEstimator.hh:210
fastjet::BackgroundJetPtMDensity::result
virtual double result(const PseudoJet &jet) const
the action of the function this has to be overloaded in derived classes
Definition: JetMedianBackgroundEstimator.hh:449
fastjet::JetMedianBackgroundEstimator::set_selector
void set_selector(const Selector &rho_range_selector)
(re)set the selector to be used for future calls to rho() etc.
Definition: JetMedianBackgroundEstimator.hh:165
fastjet::BackgroundJetPtDensity
Definition: JetMedianBackgroundEstimator.hh:403
fastjet::BackgroundEstimatorBase
Definition: BackgroundEstimatorBase.hh:49
fastjet::JetMedianBackgroundEstimator::set_use_area_4vector
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 th...
Definition: JetMedianBackgroundEstimator.hh:278
fastjet::JetDefinition
Definition: JetDefinition.hh:173
fastjet::JetMedianBackgroundEstimator::set_rescaling_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).
Definition: JetMedianBackgroundEstimator.hh:317
fastjet::PseudoJet::constituents
virtual std::vector< PseudoJet > constituents() const
retrieve the constituents.
Definition: PseudoJet.cc:566
fastjet::JetMedianBackgroundEstimator
Definition: JetMedianBackgroundEstimator.hh:78
fastjet::JetMedianBackgroundEstimator::empty_area
double empty_area() const
Returns the estimate of the area (within the range defined by the selector) that is not occupied by j...
Definition: JetMedianBackgroundEstimator.hh:235
fastjet::BackgroundJetPtMDensity
Definition: JetMedianBackgroundEstimator.hh:447
fastjet::PseudoJet::perp
double perp() const
returns the scalar transverse momentum
Definition: PseudoJet.hh:141
fastjet::AreaDefinition
Definition: AreaDefinition.hh:80
fastjet::BackgroundJetScalarPtDensity
Definition: JetMedianBackgroundEstimator.hh:420
fastjet::FunctionOfPseudoJet< double >
fastjet::JetMedianBackgroundEstimator::n_jets_used
unsigned int n_jets_used() const
returns the number of jets used to actually compute the background properties in the last call of rho...
Definition: JetMedianBackgroundEstimator.hh:217
fastjet::JetMedianBackgroundEstimator::n_empty_jets
double n_empty_jets() const
Returns the number of empty jets used when computing the background properties.
Definition: JetMedianBackgroundEstimator.hh:251
fastjet::PseudoJet::area_4vector
virtual PseudoJet area_4vector() const
return the jet 4-vector area.
Definition: PseudoJet.cc:718
fastjet::JetMedianBackgroundEstimator::use_area_4vector
bool use_area_4vector() const
check if the estimator uses the 4-vector area or the scalar area
Definition: JetMedianBackgroundEstimator.hh:284
fastjet::JetMedianBackgroundEstimator::jet_density_class
const FunctionOfPseudoJet< double > * jet_density_class() const
return the pointer to the jet density class
Definition: JetMedianBackgroundEstimator.hh:305
fastjet::BackgroundJetPtDensity::result
virtual double result(const PseudoJet &jet) const
the action of the function this has to be overloaded in derived classes
Definition: JetMedianBackgroundEstimator.hh:405
fastjet::PseudoJet
Definition: PseudoJet.hh:65
fastjet::ClusterSequenceAreaBase
Definition: ClusterSequenceAreaBase.hh:45
fastjet::Selector
Definition: Selector.hh:141
fastjet::JetMedianBackgroundEstimator::has_sigma
virtual bool has_sigma()
returns true if this background estimator has support for determination of sigma
Definition: JetMedianBackgroundEstimator.hh:201
fastjet::BackgroundJetScalarPtDensity::BackgroundJetScalarPtDensity
BackgroundJetScalarPtDensity()
Default constructor provides background estimation with scalar pt sum.
Definition: JetMedianBackgroundEstimator.hh:423
fastjet::JetMedianBackgroundEstimator::JetMedianBackgroundEstimator
JetMedianBackgroundEstimator(const Selector &rho_range=SelectorIdentity())
Default constructor that optionally sets the rho range.
Definition: JetMedianBackgroundEstimator.hh:122
fastjet::BackgroundJetScalarPtDensity::BackgroundJetScalarPtDensity
BackgroundJetScalarPtDensity(double n)
Constructor to provide background estimation based on .
Definition: JetMedianBackgroundEstimator.hh:427
fastjet::JetMedianBackgroundEstimator::set_provide_fj2_sigma
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...
Definition: JetMedianBackgroundEstimator.hh:290