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Last change on this file since 6f9baba was 35cdc46, checked in by Pavel Demin <demin@…>, 10 years ago

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[d7d2da3]1#ifndef __FASTJET_BACKGROUND_ESTIMATOR_HH__
2#define __FASTJET_BACKGROUND_ESTIMATOR_HH__
3
[35cdc46]4//FJSTARTHEADER
5// $Id: JetMedianBackgroundEstimator.hh 3517 2014-08-01 14:23:13Z soyez $
[d7d2da3]6//
[35cdc46]7// Copyright (c) 2005-2014, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
[d7d2da3]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
[35cdc46]18// development. They are described in the original FastJet paper,
19// hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
[d7d2da3]20// FastJet as part of work towards a scientific publication, please
[35cdc46]21// quote the version you use and include a citation to the manual and
22// optionally also to hep-ph/0512210.
[d7d2da3]23//
24// FastJet is distributed in the hope that it will be useful,
25// but WITHOUT ANY WARRANTY; without even the implied warranty of
26// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
27// GNU General Public License for more details.
28//
29// You should have received a copy of the GNU General Public License
30// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
31//----------------------------------------------------------------------
[35cdc46]32//FJENDHEADER
[d7d2da3]33
34#include <fastjet/ClusterSequenceAreaBase.hh>
35#include <fastjet/AreaDefinition.hh>
36#include <fastjet/FunctionOfPseudoJet.hh>
37#include <fastjet/Selector.hh>
38#include <fastjet/tools/BackgroundEstimatorBase.hh>
39#include <iostream>
40
41FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
42
43
44/// @ingroup tools_background
45/// \class JetMedianBackgroundEstimator
46///
47/// Class to estimate the pt density of the background per unit area,
48/// using the median of the distribution of pt/area from jets that
49/// pass some selection criterion.
50///
51/// Events are passed either in the form of the event particles (in
52/// which they're clustered by the class), a ClusterSequenceArea (in
53/// which case the jets used are those returned by "inclusive_jets()")
54/// or directly as a set of jets.
55///
56/// The selection criterion is typically a geometrical one (e.g. all
57/// jets with |y|<2) sometimes supplemented with some kinematical
58/// restriction (e.g. exclusion of the two hardest jets). It is passed
59/// to the class through a Selector.
60///
61/// Beware:
62/// by default, to correctly handle partially empty events, the
63/// class attempts to calculate an "empty area", based
64/// (schematically) on
65///
66/// range.total_area() - sum_{jets_in_range} jets.area()
67///
68/// For ranges with small areas, this can be inaccurate (particularly
69/// relevant in dense events where empty_area should be zero and ends
70/// up not being zero).
71///
72/// This calculation of empty area can be avoided if a
73/// ClusterSequenceArea class with explicit ghosts
74/// (ActiveAreaExplicitGhosts) is used. This is _recommended_
75/// unless speed requirements cause you to use Voronoi areas. For
76/// speedy background estimation you could also consider using
77/// GridMedianBackgroundEstimator.
78///
79///
80class JetMedianBackgroundEstimator : public BackgroundEstimatorBase {
81public:
82 /// @name constructors and destructors
83 //\{
84 //----------------------------------------------------------------
85 /// Constructor that sets the rho range as well as the jet
86 /// definition and area definition to be used to cluster the
87 /// particles. Prior to the estimation of rho, one has to provide
88 /// the particles to cluster using set_particles(...)
89 ///
90 /// \param rho_range the Selector specifying which jets will be considered
91 /// \param jet_def the jet definition to use for the clustering
92 /// \param area_def the area definition to use for the clustering
93 JetMedianBackgroundEstimator(const Selector &rho_range,
94 const JetDefinition &jet_def,
95 const AreaDefinition &area_def);
96
97 /// ctor from a ClusterSequenceAreaBase with area
98 ///
99 /// \param rho_range the Selector specifying which jets will be considered
100 /// \param csa the ClusterSequenceArea to use
101 ///
102 /// Pre-conditions:
103 /// - one should be able to estimate the "empty area" (i.e. the area
104 /// not occupied by jets). This is feasible if at least one of the following
105 /// conditions is satisfied:
106 /// ( i) the ClusterSequence has explicit ghosts
107 /// (ii) the range has a computable area.
108 /// - the jet algorithm must be suited for median computation
109 /// (otherwise a warning will be issues)
110 ///
111 /// Note that selectors with e.g. hardest-jets exclusion do not have
112 /// a well-defined area. For this reasons, it is STRONGLY advised to
113 /// use an area with explicit ghosts.
114 JetMedianBackgroundEstimator(const Selector &rho_range,
115 const ClusterSequenceAreaBase &csa);
116
117
118 /// Default constructor that optionally sets the rho range. The
119 /// configuration must be done later calling
120 /// set_cluster_sequence(...) or set_jets(...).
121 ///
122 /// \param rho_range the Selector specifying which jets will be considered
123 ///
124 JetMedianBackgroundEstimator(const Selector &rho_range = SelectorIdentity())
[35cdc46]125 : _rho_range(rho_range), _jet_def(JetDefinition()),
126 _enable_rho_m(true){ reset(); }
[d7d2da3]127
128
129 /// default dtor
130 ~JetMedianBackgroundEstimator(){}
131
132 //\}
133
134
135 /// @name setting a new event
136 //\{
137 //----------------------------------------------------------------
138
139 /// tell the background estimator that it has a new event, composed
140 /// of the specified particles.
141 virtual void set_particles(const std::vector<PseudoJet> & particles);
142
143 /// (re)set the cluster sequence (with area support) to be used by
144 /// future calls to rho() etc.
145 ///
146 /// \param csa the cluster sequence area
147 ///
148 /// Pre-conditions:
149 /// - one should be able to estimate the "empty area" (i.e. the area
150 /// not occupied by jets). This is feasible if at least one of the following
151 /// conditions is satisfied:
152 /// ( i) the ClusterSequence has explicit ghosts
153 /// (ii) the range selected has a computable area.
154 /// - the jet algorithm must be suited for median computation
155 /// (otherwise a warning will be issues)
156 ///
157 /// Note that selectors with e.g. hardest-jets exclusion do not have
158 /// a well-defined area. For this reasons, it is STRONGLY advised to
159 /// use an area with explicit ghosts.
160 void set_cluster_sequence(const ClusterSequenceAreaBase & csa);
161
162 /// (re)set the jets (which must have area support) to be used by future
163 /// calls to rho() etc.; for the conditions that must be satisfied
164 /// by the jets, see the Constructor that takes jets.
165 void set_jets(const std::vector<PseudoJet> &jets);
166
167 /// (re)set the selector to be used for future calls to rho() etc.
168 void set_selector(const Selector & rho_range_selector) {
169 _rho_range = rho_range_selector;
170 _uptodate = false;
171 }
172
[35cdc46]173 /// determine whether the automatic calculation of rho_m and sigma_m
174 /// is enabled (by default true)
175 void set_compute_rho_m(bool enable){ _enable_rho_m = enable;}
176
[d7d2da3]177 //\}
178
179
180 /// @name retrieving fundamental information
181 //\{
182 //----------------------------------------------------------------
183
184 /// get rho, the median background density per unit area
185 double rho() const;
186
187 /// get sigma, the background fluctuations per unit area
188 double sigma() const;
189
190 /// get rho, the median background density per unit area, locally at
191 /// the position of a given jet.
192 ///
193 /// If the Selector associated with the range takes a reference jet
194 /// (i.e. is relocatable), then for subsequent operations the
195 /// Selector has that jet set as its reference.
196 double rho(const PseudoJet & jet);
197
198 /// get sigma, the background fluctuations per unit area,
199 /// locally at the position of a given jet.
200 ///
201 /// If the Selector associated with the range takes a reference jet
202 /// (i.e. is relocatable), then for subsequent operations the
203 /// Selector has that jet set as its reference.
204 double sigma(const PseudoJet &jet);
205
206 /// returns true if this background estimator has support for
207 /// determination of sigma
208 virtual bool has_sigma() {return true;}
209
[35cdc46]210 //----------------------------------------------------------------
211 // now do the same thing for rho_m and sigma_m
212
213 /// returns rho_m, the purely longitudinal, particle-mass-induced
214 /// component of the background density per unit area
215 virtual double rho_m() const;
216
217 /// returns sigma_m, a measure of the fluctuations in the purely
218 /// longitudinal, particle-mass-induced component of the background
219 /// density per unit area; must be multipled by sqrt(area) to get
220 /// fluctuations for a region of a given area.
221 virtual double sigma_m() const;
222
223 /// Returns rho_m locally at the jet position. As for rho(jet), it is non-const.
224 virtual double rho_m(const PseudoJet & /*jet*/);
225
226 /// Returns sigma_m locally at the jet position. As for rho(jet), it is non-const.
227 virtual double sigma_m(const PseudoJet & /*jet*/);
228
229 /// Returns true if this background estimator has support for
230 /// determination of rho_m.
231 ///
232 /// In te presence of a density class, support for rho_m is
233 /// automatically disabled
234 ///
235 /// Note that support for sigma_m is automatic is one has sigma and
236 /// rho_m support.
237 virtual bool has_rho_m() const {return _enable_rho_m && (_jet_density_class == 0);}
[d7d2da3]238 //\}
239
240 /// @name retrieving additional useful information
241 //\{
242 //----------------------------------------------------------------
243 /// Returns the mean area of the jets used to actually compute the
244 /// background properties in the last call of rho() or sigma()
[35cdc46]245 /// If the configuration has changed in the meantime, throw an error.
[d7d2da3]246 double mean_area() const{
[35cdc46]247 if (!_uptodate)
248 throw Error("JetMedianBackgroundEstimator::mean_area(): one may not retrieve information about the last call to rho() or sigma() when the configuration has changed in the meantime.");
249 //_recompute_if_needed();
[d7d2da3]250 return _mean_area;
251 }
252
253 /// returns the number of jets used to actually compute the
254 /// background properties in the last call of rho() or sigma()
[35cdc46]255 /// If the configuration has changed in the meantime, throw an error.
[d7d2da3]256 unsigned int n_jets_used() const{
[35cdc46]257 if (!_uptodate)
258 throw Error("JetMedianBackgroundEstimator::n_jets_used(): one may not retrieve information about the last call to rho() or sigma() when the configuration has changed in the meantime.");
259 //_recompute_if_needed();
[d7d2da3]260 return _n_jets_used;
261 }
262
[35cdc46]263 /// returns the jets used to actually compute the background
264 /// properties
265 std::vector<PseudoJet> jets_used() const{
266 if (!_uptodate) throw Error("JetMedianBackgroundEstimator::n_jets_used(): one may not retrieve information about the last call to rho() or sigma() when the configuration has changed in the meantime.");
267 _check_csa_alive();
268 std::vector<PseudoJet> tmp_jets = _rho_range(_included_jets);
269 std::vector<PseudoJet> used_jets;
270 for (unsigned int i=0; i<tmp_jets.size(); i++){
271 if (tmp_jets[i].area()>0) used_jets.push_back(tmp_jets[i]);
272 }
273 return used_jets;
274 }
275
[d7d2da3]276 /// Returns the estimate of the area (within the range defined by
277 /// the selector) that is not occupied by jets. The value is that
278 /// for the last call of rho() or sigma()
[35cdc46]279 /// If the configuration has changed in the meantime, throw an error.
[d7d2da3]280 ///
281 /// The answer is defined to be zero if the area calculation
282 /// involved explicit ghosts; if the area calculation was an active
283 /// area, then use is made of the active area's internal list of
284 /// pure ghost jets (taking those that pass the selector); otherwise
285 /// it is based on the difference between the selector's total area
286 /// and the area of the jets that pass the selector.
287 ///
288 /// The result here is just the cached result of the corresponding
289 /// call to the ClusterSequenceAreaBase function.
290 double empty_area() const{
[35cdc46]291 if (!_uptodate)
292 throw Error("JetMedianBackgroundEstimator::empty_area(): one may not retrieve information about the last call to rho() or sigma() when the configuration has changed in the meantime.");
293 //_recompute_if_needed();
[d7d2da3]294 return _empty_area;
295 }
296
297 /// Returns the number of empty jets used when computing the
298 /// background properties. The value is that for the last call of
299 /// rho() or sigma().
[35cdc46]300 /// If the configuration has changed in the meantime, throw an error.
[d7d2da3]301 ///
302 /// If the area has explicit ghosts the result is zero; for active
303 /// areas it is the number of internal pure ghost jets that pass the
304 /// selector; otherwise it is deduced from the empty area, divided by
305 /// \f$ 0.55 \pi R^2 \f$ (the average pure-ghost-jet area).
306 ///
307 /// The result here is just the cached result of the corresponding
308 /// call to the ClusterSequenceAreaBase function.
309 double n_empty_jets() const{
[35cdc46]310 if (!_uptodate)
311 throw Error("JetMedianBackgroundEstimator::n_empty_jets(): one may not retrieve information about the last call to rho() or sigma() when the configuration has changed in the meantime.");
312 //_recompute_if_needed();
[d7d2da3]313 return _n_empty_jets;
314 }
315
316 //}
317
318
319 /// @name configuring behaviour
320 //\{
321 //----------------------------------------------------------------
322
323 /// Resets the class to its default state, including the choice to
324 /// use 4-vector areas.
325 ///
326 void reset();
327
328 /// By default when calculating pt/Area for a jet, it is the
329 /// transverse component of the 4-vector area that is used in the ratiof \f$p_t/A\f$.
330 /// Calling this function with a "false" argument causes the scalar area to
331 /// be used instead.
332 ///
333 /// While the difference between the two choices is usually small,
334 /// for high-precision work it is usually the 4-vector area that is
335 /// to be preferred.
336 ///
337 /// \param use_it whether one uses the 4-vector area or not (true by default)
338 void set_use_area_4vector(bool use_it = true){
339 _use_area_4vector = use_it;
340 _uptodate = false;
341 }
342
343 /// check if the estimator uses the 4-vector area or the scalar area
344 bool use_area_4vector() const{ return _use_area_4vector;}
345
346 /// The FastJet v2.X sigma calculation had a small spurious offset
347 /// in the limit of a small number of jets. This is fixed by default
348 /// in versions 3 upwards. The old behaviour can be obtained with a
349 /// call to this function.
350 void set_provide_fj2_sigma(bool provide_fj2_sigma = true) {
351 _provide_fj2_sigma = provide_fj2_sigma;
352 _uptodate = false;
353 }
354
355 /// Set a pointer to a class that calculates the quantity whose
356 /// median will be calculated; if the pointer is null then pt/area
357 /// is used (as occurs also if this function is not called).
358 ///
359 /// Note that this is still <i>preliminary</i> in FastJet 3.0 and
360 /// that backward compatibility is not guaranteed in future releases
361 /// of FastJet
362 void set_jet_density_class(const FunctionOfPseudoJet<double> * jet_density_class);
363
364 /// return the pointer to the jet density class
365 const FunctionOfPseudoJet<double> * jet_density_class() const{
366 return _jet_density_class;
367 }
368
369 /// Set a pointer to a class that calculates the rescaling factor as
370 /// a function of the jet (position). Note that the rescaling factor
371 /// is used both in the determination of the "global" rho (the pt/A
372 /// of each jet is divided by this factor) and when asking for a
373 /// local rho (the result is multiplied by this factor).
374 ///
375 /// The BackgroundRescalingYPolynomial class can be used to get a
376 /// rescaling that depends just on rapidity.
377 virtual void set_rescaling_class(const FunctionOfPseudoJet<double> * rescaling_class_in) {
378 BackgroundEstimatorBase::set_rescaling_class(rescaling_class_in);
379 _uptodate = false;
380 }
381
382 //\}
383
384 /// @name description
385 //\{
386 //----------------------------------------------------------------
387
388 /// returns a textual description of the background estimator
389 std::string description() const;
390
391 //\}
392
393
394private:
395
396 /// do the actual job
397 void _compute() const;
398
399 /// check if the properties need to be recomputed
400 /// and do so if needed
401 void _recompute_if_needed() const {
402 if (!_uptodate) _compute();
403 _uptodate = true;
404 }
405
406 /// for estimation using a selector that takes a reference jet
407 /// (i.e. a selector that can be relocated) this function allows one
408 /// to set its position.
409 ///
410 /// Note that this HAS to be called before any attempt to compute
411 /// the background properties. The call is, however, performed
412 /// automatically by the functions rho(jet) and sigma(jet).
413 void _recompute_if_needed(const PseudoJet &jet);
414
415 /// check that the underlying structure is still alive
416 /// throw an error otherwise
417 void _check_csa_alive() const;
418
419 /// check that the algorithm used for the clustering is adapted for
420 /// background estimation (i.e. either kt or C/A)
421 /// Issue a warning otherwise
422 void _check_jet_alg_good_for_median() const;
[35cdc46]423
[d7d2da3]424 // the basic parameters of this class (passed through the variou ctors)
425 Selector _rho_range; ///< range to compute the background in
426 JetDefinition _jet_def; ///< the jet def to use for teh clustering
427 AreaDefinition _area_def; ///< the area def to use for teh clustering
428 std::vector<PseudoJet> _included_jets; ///< jets to be used
429
[35cdc46]430 // the tunable parameters of the class
[d7d2da3]431 bool _use_area_4vector;
432 bool _provide_fj2_sigma;
433 const FunctionOfPseudoJet<double> * _jet_density_class;
434 //SharedPtr<BackgroundRescalingBase> _rescaling_class_sharedptr;
[35cdc46]435 bool _enable_rho_m;
[d7d2da3]436
437 // the actual results of the computation
438 mutable double _rho; ///< background estimated density per unit area
439 mutable double _sigma; ///< background estimated fluctuations
[35cdc46]440 mutable double _rho_m; ///< "mass" background estimated density per unit area
441 mutable double _sigma_m; ///< "mass" background estimated fluctuations
[d7d2da3]442 mutable double _mean_area; ///< mean area of the jets used to estimate the background
443 mutable unsigned int _n_jets_used; ///< number of jets used to estimate the background
444 mutable double _n_empty_jets; ///< number of empty (pure-ghost) jets
445 mutable double _empty_area; ///< the empty (pure-ghost/unclustered) area!
446
447 // internal variables
448 SharedPtr<PseudoJetStructureBase> _csi; ///< allows to check if _csa is still valid
449 PseudoJet _current_reference; ///< current reference jet
450 mutable bool _uptodate; ///< true when the background computation is up-to-date
451
452 /// handle warning messages
453 static LimitedWarning _warnings;
454 static LimitedWarning _warnings_zero_area;
455 static LimitedWarning _warnings_preliminary;
456};
457
458
459
460
461//----------------------------------------------------------------------
462/// @ingroup tools_background
463/// \class BackgroundJetPtDensity
464/// Class that implements pt/area_4vector.perp() for background estimation
465/// <i>(this is a preliminary class)</i>.
466class BackgroundJetPtDensity : public FunctionOfPseudoJet<double> {
467public:
468 virtual double result(const PseudoJet & jet) const {
469 return jet.perp() / jet.area_4vector().perp();
470 }
471 virtual std::string description() const {return "BackgroundJetPtDensity";}
472};
473
474
475//----------------------------------------------------------------------
476/// @ingroup tools_background
477/// \class BackgroundJetScalarPtDensity
478/// Class that implements (scalar pt sum of jet)/(scalar area of jet)
479/// for background estimation <i>(this is a preliminary class)</i>.
480///
481/// Optionally it can return a quantity based on the sum of pt^n,
482/// e.g. for use in subtracting fragementation function moments.
483class BackgroundJetScalarPtDensity : public FunctionOfPseudoJet<double> {
484public:
485 /// Default constructor provides background estimation with scalar pt sum
486 BackgroundJetScalarPtDensity() : _pt_power(1) {}
487
488 /// Constructor to provide background estimation based on
489 /// \f$ sum_{i\in jet} p_{ti}^{n} \f$
490 BackgroundJetScalarPtDensity(double n) : _pt_power(n) {}
491
492 virtual double result(const PseudoJet & jet) const;
493
[35cdc46]494 virtual std::string description() const;
[d7d2da3]495
496private:
497 double _pt_power;
498};
499
500//----------------------------------------------------------------------
501/// @ingroup tools_background
502/// \class BackgroundJetPtMDensity
503/// Class that implements
504/// \f$ \frac{1}{A} \sum_{i \in jet} (\sqrt{p_{ti}^2+m^2} - p_{ti}) \f$
505/// for background estimation <i>(this is a preliminary class)</i>.
506///
507///
508/// This is useful for correcting jet masses in cases where the event
509/// involves massive particles.
510class BackgroundJetPtMDensity : public FunctionOfPseudoJet<double> {
511public:
512 virtual double result(const PseudoJet & jet) const {
513 std::vector<PseudoJet> constituents = jet.constituents();
514 double scalar_ptm = 0;
515 for (unsigned i = 0; i < constituents.size(); i++) {
516 scalar_ptm += constituents[i].mperp() - constituents[i].perp();
517 }
518 return scalar_ptm / jet.area();
519 }
520
521 virtual std::string description() const {return "BackgroundPtMDensity";}
522};
523
524
525
526FASTJET_END_NAMESPACE
527
528#endif // __BACKGROUND_ESTIMATOR_HH__
529
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