fastjet::SISConePlugin Class Reference

SISConePlugin is a plugin for fastjet (v2.1 upwards) that provides an interface to the seedless infrared safe cone jet finder by Gregory Soyez and Gavin Salam. More...

#include <SISConePlugin.hh>

Inheritance diagram for fastjet::SISConePlugin:

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Collaboration diagram for fastjet::SISConePlugin:

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List of all members.

Public Types
enum	SplitMergeScale { SM_pt, SM_Et, SM_mt, SM_pttilde }
	enum for the different split-merge scale choices; Note that order _must_ be the same as in siscone More...
Public Member Functions
	SISConePlugin (double cone_radius, double overlap_threshold, int n_pass_max=0, double protojet_ptmin=0.0, bool caching=false, SplitMergeScale split_merge_scale=SM_pttilde, double split_merge_stopping_scale=0.0)
	Main constructor for the SISCone Plugin class.
	SISConePlugin (double cone_radius, double overlap_threshold, int n_pass_max, double protojet_ptmin, bool caching, bool split_merge_on_transverse_mass)
	Backwards compatible constructor for the SISCone Plugin class.
	SISConePlugin (double cone_radius, double overlap_threshold, int n_pass_max, bool caching)
	backwards compatible constructor for the SISCone Plugin class (avoid using this in future).
double	protojet_ptmin () const
	minimum pt for a protojet to be considered in the split-merge step of the algorithm
double	protojet_or_ghost_ptmin () const
	return the scale to be passed to SISCone as the protojet_ptmin -- if we have a ghost separation scale that is above the protojet_ptmin, then the ghost_separation_scale becomes the relevant one to use here
SplitMergeScale	split_merge_scale () const
	indicates scale used in split-merge
void	set_split_merge_scale (SplitMergeScale sms)
	sets scale used in split-merge
bool	split_merge_on_transverse_mass () const
	indicates whether the split-merge orders on transverse mass or not.
void	set_split_merge_on_transverse_mass (bool val)
bool	split_merge_use_pt_weighted_splitting () const
	indicates whether the split-merge orders on transverse mass or not.
void	set_split_merge_use_pt_weighted_splitting (bool val)
virtual std::string	description () const
	plugin description
virtual void	run_clustering (ClusterSequence &) const
	really do the clustering work
Protected Member Functions
virtual void	reset_stored_plugin () const
	call the re-clustering itself
Private Attributes
double	_protojet_ptmin
SplitMergeScale	_split_merge_scale
bool	_use_pt_weighted_splitting
Static Private Attributes
static std::auto_ptr < SISConePlugin >	stored_plugin
static std::auto_ptr < std::vector< PseudoJet > >	stored_particles
static std::auto_ptr < siscone::Csiscone >	stored_siscone

---

Detailed Description

SISConePlugin is a plugin for fastjet (v2.1 upwards) that provides an interface to the seedless infrared safe cone jet finder by Gregory Soyez and Gavin Salam.

SISCone uses geometrical techniques to exhaustively consider all possible distinct cones. It then finds out which ones are stable and sends the result to the Tevatron Run-II type split-merge procedure for overlapping cones.

Four parameters govern the "physics" of the algorithm:

• the cone_radius (this should be self-explanatory!)

• the overlap_threshold is the parameter which dictates how much two jets must overlap (pt_overlap/min(pt1,pt2)) if they are to be merged

• Not all particles are in stable cones in the first round of searching for stable cones; one can therefore optionally have the the jet finder carry out additional passes of searching for stable cones among particles that were in no stable cone in previous passes --- the maximum number of passes carried out is n_pass_max. If this is zero then additional passes are carried out until no new stable cones are found.

• Protojet ptmin: protojets that are below this ptmin (default = 0) are discarded before each iteration of the split-merge loop.

One parameter governs some internal algorithmic shortcuts:

• if "caching" is turned on then the last event clustered by siscone is stored -- if the current event is identical and the cone_radius and n_pass_mass are identical, then the only part of the clustering that needs to be rerun is the split-merge part, leading to significant speed gains; there is a small (O(N) storage and speed) penalty for caching, so it should be kept off (default) if only a single overlap_threshold is used.

The final jets can be accessed by requestion the inclusive_jets(...) from the ClusterSequence object. Note that these PseudoJets have their user_index() set to the index of the pass in which they were found (first pass = 0). NB: This does not currently work for jets that consist of a single particle.

For further information on the details of the algorithm see the SISCone paper, arXiv:0704.0292 [JHEP 0705:086,2007].

For documentation about the implementation, see the siscone/doc/html/index.html file.

Definition at line 67 of file SISConePlugin.hh.

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Member Enumeration Documentation

enum fastjet::SISConePlugin::SplitMergeScale

enum for the different split-merge scale choices; Note that order _must_ be the same as in siscone

Enumerator:

SM_pt	transverse momentum (E-scheme), IR unsafe
SM_Et	transverse energy (E-scheme), not long. boost invariant original run-II choice [may not be implemented]
SM_mt	transverse mass (E-scheme), IR safe except in decays of two identical narrow heavy particles
SM_pttilde	pt-scheme pt = {i in jet} |p_{ti}|, should be IR safe in all cases

Definition at line 72 of file SISConePlugin.hh.

                       {SM_pt,     
                        SM_Et,     

                        SM_mt,     

                        SM_pttilde 

  };

---

Constructor & Destructor Documentation

fastjet::SISConePlugin::SISConePlugin	(	double	cone_radius,
		double	overlap_threshold,
		int	n_pass_max = 0,
		double	protojet_ptmin = 0.0,
		bool	caching = false,
		SplitMergeScale	split_merge_scale = SM_pttilde,
		double	split_merge_stopping_scale = 0.0
	)			[inline]

Main constructor for the SISCone Plugin class.

Note: wrt version prior to 2.4 this constructor differs in that a the default value has been removed for overlap_threshold. The former has been removed because the old default of 0.5 was found to be unsuitable in high-noise environments; so the user should now explicitly think about the value for this -- we recommend 0.75.

Definition at line 91 of file SISConePlugin.hh.

Referenced by reset_stored_plugin().

                                                         {
    _cone_radius           = cone_radius;
    _overlap_threshold     = overlap_threshold;
    _n_pass_max            = n_pass_max;
    _protojet_ptmin        = protojet_ptmin;
    _caching               = caching;   
    _split_merge_scale     = split_merge_scale;
    _split_merge_stopping_scale = split_merge_stopping_scale;
    _ghost_sep_scale       = 0.0;
    _use_pt_weighted_splitting = false;}

fastjet::SISConePlugin::SISConePlugin	(	double	cone_radius,
		double	overlap_threshold,
		int	n_pass_max,
		double	protojet_ptmin,
		bool	caching,
		bool	split_merge_on_transverse_mass
	)			[inline]

Backwards compatible constructor for the SISCone Plugin class.

Definition at line 110 of file SISConePlugin.hh.

                                                       {
    _cone_radius           = cone_radius;
    _overlap_threshold     = overlap_threshold;
    _n_pass_max            = n_pass_max;
    _protojet_ptmin        = protojet_ptmin;
    _caching               = caching;   
    _split_merge_stopping_scale = 0.0;
    _split_merge_scale     = split_merge_on_transverse_mass ? SM_mt : SM_pttilde;
    _ghost_sep_scale       = 0.0;}

fastjet::SISConePlugin::SISConePlugin	(	double	cone_radius,
		double	overlap_threshold,
		int	n_pass_max,
		bool	caching
	)			[inline]

backwards compatible constructor for the SISCone Plugin class (avoid using this in future).

Definition at line 127 of file SISConePlugin.hh.

                                  {
    _cone_radius           = cone_radius;
    _overlap_threshold     = overlap_threshold;
    _n_pass_max            = n_pass_max;
    _protojet_ptmin        = 0.0;
    _caching               = caching;   
    _split_merge_scale     = SM_mt;
    _split_merge_stopping_scale = 0.0;
    _ghost_sep_scale       = 0.0;
    _use_pt_weighted_splitting = false;}

---

Member Function Documentation

string fastjet::SISConePlugin::description

(

)

const [virtual]

plugin description

Implements fastjet::SISConeBasePlugin.

Definition at line 36 of file SISConePlugin.cc.

References fastjet::SISConeBasePlugin::_split_merge_stopping_scale, fastjet::SISConeBasePlugin::_use_jet_def_recombiner, _use_pt_weighted_splitting, fastjet::SISConeBasePlugin::caching(), fastjet::SISConeBasePlugin::cone_radius(), fastjet::SISConeBasePlugin::n_pass_max(), fastjet::SISConeBasePlugin::overlap_threshold(), protojet_ptmin(), and split_merge_scale().

                                         {
  ostringstream desc;
  
  const string on = "on";
  const string off = "off";

  string sm_scale_string = "split-merge uses " + 
    split_merge_scale_name(Esplit_merge_scale(split_merge_scale()));

  desc << "SISCone jet algorithm with " ;
  desc << "cone_radius = "       << cone_radius        () << ", ";
  desc << "overlap_threshold = " << overlap_threshold  () << ", ";
  desc << "n_pass_max = "        << n_pass_max         () << ", ";
  desc << "protojet_ptmin = "    << protojet_ptmin()      << ", ";
  desc <<  sm_scale_string                                << ", ";
  desc << "caching turned "      << (caching() ? on : off);
  desc << ", SM stop scale = "     << _split_merge_stopping_scale;

  // add a note to the description if we use the pt-weighted splitting
  if (_use_pt_weighted_splitting){
    desc << ", using pt-weighted splitting";
  }

  if (_use_jet_def_recombiner){
    desc << ", using jet-definition's own recombiner";
  }

  // create a fake siscone object so that we can find out more about it
  Csiscone siscone;
  if (siscone.merge_identical_protocones) {
    desc << ", and (IR unsafe) merge_indentical_protocones=true" ;
  }

  desc << ", SISCone code v" << siscone_version();

  return desc.str();
}

double fastjet::SISConePlugin::protojet_or_ghost_ptmin

(

)

const [inline]

return the scale to be passed to SISCone as the protojet_ptmin -- if we have a ghost separation scale that is above the protojet_ptmin, then the ghost_separation_scale becomes the relevant one to use here

Definition at line 149 of file SISConePlugin.hh.

Referenced by run_clustering().

                                           {return std::max(_protojet_ptmin,
                                                            _ghost_sep_scale);}

double fastjet::SISConePlugin::protojet_ptmin

(

)

const [inline]

minimum pt for a protojet to be considered in the split-merge step of the algorithm

Definition at line 143 of file SISConePlugin.hh.

Referenced by description().

{return _protojet_ptmin  ;}

void fastjet::SISConePlugin::reset_stored_plugin

(

)

const [protected, virtual]

call the re-clustering itself

Implements fastjet::SISConeBasePlugin.

Definition at line 210 of file SISConePlugin.cc.

References SISConePlugin(), and stored_plugin.

Referenced by run_clustering().

                                             {
  stored_plugin.reset( new SISConePlugin(*this));
}

void fastjet::SISConePlugin::run_clustering

(

ClusterSequence &

)

const [virtual]

really do the clustering work

Implements fastjet::SISConeBasePlugin.

Definition at line 76 of file SISConePlugin.cc.

References fastjet::SISConeBaseExtras::_jet_def_plugin, fastjet::SISConeBaseExtras::_most_ambiguous_split, fastjet::SISConeBaseExtras::_pass, fastjet::SISConeBaseExtras::_protocones, fastjet::SISConeBasePlugin::_split_merge_stopping_scale, fastjet::SISConeBasePlugin::_use_jet_def_recombiner, _use_pt_weighted_splitting, fastjet::SISConeBasePlugin::caching(), fastjet::SISConeBasePlugin::cone_radius(), PseudoJet::E(), fastjet::SISConeBasePlugin::ghost_separation_scale(), have_same_momentum(), ClusterSequence::jets(), fastjet::SISConeBasePlugin::n_pass_max(), fastjet::SISConeBasePlugin::overlap_threshold(), ClusterSequence::plugin_associate_extras(), ClusterSequence::plugin_record_iB_recombination(), ClusterSequence::plugin_record_ij_recombination(), protojet_or_ghost_ptmin(), PseudoJet::px(), PseudoJet::py(), PseudoJet::pz(), reset_stored_plugin(), PseudoJet::set_user_index(), split_merge_scale(), stored_particles, stored_plugin, and stored_siscone.

                                                                    {

  Csiscone   local_siscone;
  Csiscone * siscone;
  
  unsigned n = clust_seq.jets().size();

  bool new_siscone = true; // by default we'll be running it

  if (caching()) {

    // Establish if we have a cached run with the same R, npass and
    // particles. If not then do any tidying up / reallocation that's
    // necessary for the next round of caching, otherwise just set
    // relevant pointers so that we can reuse and old run.
    if (stored_siscone.get() != 0) {
      new_siscone = !(stored_plugin->cone_radius()   == cone_radius()
                      && stored_plugin->n_pass_max() == n_pass_max()  
                      && stored_particles->size()    == n);
      if (!new_siscone) {
        for(unsigned i = 0; i < n; i++) {
          // only check momentum because indices will be correctly dealt
          // with anyway when extracting the clustering order.
          new_siscone |= !have_same_momentum(clust_seq.jets()[i], 
                                             (*stored_particles)[i]);
        }
      }
    } 
      
    // allocate the new siscone, etc., if need be
    if (new_siscone) {
      stored_siscone  .reset( new Csiscone );
      stored_particles.reset( new std::vector<PseudoJet>(clust_seq.jets()));
      reset_stored_plugin();
    }

    siscone = stored_siscone.get();
  } else {
    siscone = &local_siscone;
  }

  // make sure stopping scale is set in siscone
  siscone->SM_var2_hardest_cut_off = _split_merge_stopping_scale*_split_merge_stopping_scale;

  // set the specific parameters
  // when running with ghosts for passive areas, do not put the
  // ghosts into the stable-cone search (not relevant)
  siscone->stable_cone_soft_pt2_cutoff = ghost_separation_scale()
                                         * ghost_separation_scale();
  // set the type of splitting we want (default=std one, true->pt-weighted split)
  siscone->set_pt_weighted_splitting(_use_pt_weighted_splitting);

  if (new_siscone) {
    // transfer fastjet initial particles into the siscone type
    std::vector<Cmomentum> siscone_momenta(n);
    for(unsigned i = 0; i < n; i++) {
      const PseudoJet & p = clust_seq.jets()[i]; // shorthand
      siscone_momenta[i] = Cmomentum(p.px(), p.py(), p.pz(), p.E());
    }
    
    // run the jet finding
    //cout << "plg sms: " << split_merge_scale() << endl;
    siscone->compute_jets(siscone_momenta, cone_radius(), overlap_threshold(),
                          n_pass_max(), protojet_or_ghost_ptmin(), 
                          Esplit_merge_scale(split_merge_scale()));
  } else {
    // rerun the jet finding
    // just run the overlap part of the jets.
    //cout << "plg rcmp sms: " << split_merge_scale() << endl;
    siscone->recompute_jets(overlap_threshold(), protojet_or_ghost_ptmin(), 
                            Esplit_merge_scale(split_merge_scale()));
  }

  // extract the jets [in reverse order -- to get nice ordering in pt at end]
  int njet = siscone->jets.size();

  // allocate space for the extras object
  SISConeExtras * extras = new SISConeExtras(n);

  for (int ijet = njet-1; ijet >= 0; ijet--) {
    const Cjet & jet = siscone->jets[ijet]; // shorthand
    
    // Successively merge the particles that make up the cone jet
    // until we have all particles in it.  Start off with the zeroth
    // particle.
    int jet_k = jet.contents[0];
    for (unsigned ipart = 1; ipart < jet.contents.size(); ipart++) {
      // take the last result of the merge
      int jet_i = jet_k;
      // and the next element of the jet
      int jet_j = jet.contents[ipart];
      // and merge them (with a fake dij)
      double dij = 0.0;

      if (_use_jet_def_recombiner) {
        clust_seq.plugin_record_ij_recombination(jet_i, jet_j, dij, jet_k);
      } else {
        // create the new jet by hand so that we can adjust its user index
        PseudoJet newjet = clust_seq.jets()[jet_i] + clust_seq.jets()[jet_j];
        // set the user index to be the pass in which the jet was discovered
        newjet.set_user_index(jet.pass);
        clust_seq.plugin_record_ij_recombination(jet_i, jet_j, dij, newjet, jet_k);
      }

    }

    // we have merged all the jet's particles into a single object, so now
    // "declare" it to be a beam (inclusive) jet.
    // [NB: put a sensible looking d_iB just to be nice...]
    double d_iB = clust_seq.jets()[jet_k].perp2();
    clust_seq.plugin_record_iB_recombination(jet_k, d_iB);

    // now record the pass of the jet in the extras object
    extras->_pass[clust_seq.jets()[jet_k].cluster_hist_index()] = jet.pass;
  }

  // now copy the list of protocones into an "extras" objects
  for (unsigned ipass = 0; ipass < siscone->protocones_list.size(); ipass++) {
    for (unsigned ipc = 0; ipc < siscone->protocones_list[ipass].size(); ipc++) {
      PseudoJet protocone(siscone->protocones_list[ipass][ipc]);
      protocone.set_user_index(ipass);
      extras->_protocones.push_back(protocone);
    }
  }
  extras->_most_ambiguous_split = siscone->most_ambiguous_split;

  // tell it what the jet definition was
  extras->_jet_def_plugin = this;

  // give the extras object to the cluster sequence.
  clust_seq.plugin_associate_extras(std::auto_ptr<ClusterSequence::Extras>(extras));
}

void fastjet::SISConePlugin::set_split_merge_on_transverse_mass

(

bool

val

)

[inline]

Definition at line 160 of file SISConePlugin.hh.

                                                    {
    _split_merge_scale = val  ? SM_mt : SM_pt;}

void fastjet::SISConePlugin::set_split_merge_scale

(

SplitMergeScale

sms

)

[inline]

sets scale used in split-merge

Definition at line 155 of file SISConePlugin.hh.

{_split_merge_scale = sms;}

void fastjet::SISConePlugin::set_split_merge_use_pt_weighted_splitting

(

bool

val

)

[inline]

Definition at line 166 of file SISConePlugin.hh.

                                                           {
    _use_pt_weighted_splitting = val;}

bool fastjet::SISConePlugin::split_merge_on_transverse_mass

(

)

const [inline]

indicates whether the split-merge orders on transverse mass or not.

retained for backwards compatibility with 2.1.0b3

Definition at line 159 of file SISConePlugin.hh.

{return _split_merge_scale == SM_mt ;}

SplitMergeScale fastjet::SISConePlugin::split_merge_scale

(

)

const [inline]

indicates scale used in split-merge

Definition at line 153 of file SISConePlugin.hh.

Referenced by description(), and run_clustering().

{return _split_merge_scale;}

bool fastjet::SISConePlugin::split_merge_use_pt_weighted_splitting

(

)

const [inline]

indicates whether the split-merge orders on transverse mass or not.

retained for backwards compatibility with 2.1.0b3

Definition at line 165 of file SISConePlugin.hh.

{return _use_pt_weighted_splitting;}

---

Member Data Documentation

double fastjet::SISConePlugin::_protojet_ptmin [private]

Definition at line 177 of file SISConePlugin.hh.

SplitMergeScale fastjet::SISConePlugin::_split_merge_scale [private]

Definition at line 178 of file SISConePlugin.hh.

bool fastjet::SISConePlugin::_use_pt_weighted_splitting [private]

Definition at line 180 of file SISConePlugin.hh.

Referenced by description(), and run_clustering().

std::auto_ptr< std::vector< PseudoJet > > fastjet::SISConePlugin::stored_particles [static, private]

Definition at line 185 of file SISConePlugin.hh.

Referenced by run_clustering().

std::auto_ptr< SISConePlugin > fastjet::SISConePlugin::stored_plugin [static, private]

Definition at line 184 of file SISConePlugin.hh.

Referenced by reset_stored_plugin(), and run_clustering().

std::auto_ptr< Csiscone > fastjet::SISConePlugin::stored_siscone [static, private]

Definition at line 186 of file SISConePlugin.hh.

Referenced by run_clustering().

---

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

• plugins/SISCone/fastjet/SISConePlugin.hh
• plugins/SISCone/SISConePlugin.cc