TrimmedVertexFinder.cc

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#include "RecoVertex/TrimmedKalmanVertexFinder/interface/TrimmedVertexFinder.h"
#include "CommonTools/Statistics/interface/ChiSquaredProbability.h"
#include "RecoVertex/VertexTools/interface/PerigeeLinearizedTrackState.h"
#include "FWCore/Utilities/interface/Exception.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"

using namespace reco;

TrimmedVertexFinder::TrimmedVertexFinder(const VertexFitter<5>* vf,
                                         const VertexUpdator<5>* vu,
                                         const VertexTrackCompatibilityEstimator<5>* ve)
    : theFitter(vf->clone()), theUpdator(vu->clone()), theEstimator(ve->clone()), theMinProb(0.05) {}

TrimmedVertexFinder::TrimmedVertexFinder(const TrimmedVertexFinder& other)
    : theFitter(other.theFitter->clone()),
      theUpdator(other.theUpdator->clone()),
      theEstimator(other.theEstimator->clone()),
      theMinProb(other.theMinProb) {}

TrimmedVertexFinder::~TrimmedVertexFinder() {
  delete theFitter;
  delete theUpdator;
  delete theEstimator;
}

std::vector<TransientVertex> TrimmedVertexFinder::vertices(std::vector<TransientTrack>& tks) const {
  // FIXME write this!!!
  return vertices(tks, reco::BeamSpot(), false);
}

std::vector<TransientVertex> TrimmedVertexFinder::vertices(std::vector<TransientTrack>& tks,
                                                           const reco::BeamSpot& spot,
                                                           bool use_spot) const {
  std::vector<TransientVertex> all;
  if (tks.size() < 2)
    return all;

  // prepare vertex tracks and initial vertex
  CachingVertex<5> vtx;
  if (use_spot) {
    vtx = theFitter->vertex(tks, spot);
  } else {
    vtx = theFitter->vertex(tks);
  }
  if (!vtx.isValid()) {
    edm::LogWarning("TrimmedVertexFinder") << "initial vertex invalid."
                                           << " vertex finding stops here.";
    return all;
  }

  std::vector<RefCountedVertexTrack> selected = vtx.tracks();

  // reject incompatible tracks starting from the worst
  std::vector<RefCountedVertexTrack> remain;
  bool found = false;
  while (!found && selected.size() >= 2) {
    // find track with worst compatibility
    std::vector<RefCountedVertexTrack>::iterator iWorst = theWorst(vtx, selected, theMinProb);

    if (iWorst != selected.end()) {
      // reject track
      remain.push_back(*iWorst);
      selected.erase(iWorst);

      if (selected.size() == 1) {
        // not enough tracks to build new vertices
        remain.push_back(selected.front());
      } else {
        // removing track from vertex
        // need to redo the vertex fit instead of removing the track;
        // successive removals lead to numerical problems
        // this is however quick since intermediate quantities are cached
        // in the RefCountedVertexTracks
        if (use_spot)  // && all.size()==0 )
        {
          vtx = theFitter->vertex(selected, spot);
        } else {
          vtx = theFitter->vertex(selected);
        }
        if (!vtx.isValid()) {
          edm::LogWarning("TrimmedVertexFinder") << "current vertex invalid"
                                                 << "vertex finding stops here.";
          return all;
        }

        // ref-counted tracks may have changed during the fit
        // if the linearization point has moved too much
        selected = vtx.tracks();
      }

    } else {
      // no incompatible track remains, make vertex
      found = true;
      int n_tracks_in_vertex = selected.size();

      // now return all tracks with weight < 0.5 to 'remain'.
      for (std::vector<RefCountedVertexTrack>::const_iterator t = selected.begin(); t != selected.end(); ++t) {
        if ((**t).weight() < 0.5) {
          /*
          cout << "[TrimmedVertexFinder] recycling track with weight "
               << (**t).weight() << endl;*/
          remain.push_back(*t);
          n_tracks_in_vertex--;  // one 'good' track less in the vertex
        };
      };

      if (n_tracks_in_vertex > 1) {
        all.push_back(vtx);
      } else {
        edm::LogError("TrimmedVertexFinder") << "found vertex has less than 2 tracks";
      }
    }
  }

  // modify list of incompatible tracks
  tks.clear();
  for (std::vector<RefCountedVertexTrack>::const_iterator i = remain.begin(); i != remain.end(); i++) {
    const PerigeeLinearizedTrackState* plts =
        dynamic_cast<const PerigeeLinearizedTrackState*>((**i).linearizedTrack().get());
    if (plts == nullptr) {
      throw cms::Exception("TrimmedVertexFinder: can't take track from non-perigee track state");
    }

    tks.push_back(plts->track());
  }

  // return 0 or 1 vertex
  return all;
}

std::vector<TrimmedVertexFinder::RefCountedVertexTrack>::iterator TrimmedVertexFinder::theWorst(
    const CachingVertex<5>& vtx, std::vector<RefCountedVertexTrack>& vtxTracks, float cut) const {
  //  cout << "Cut is now " << cut << endl;

  // find track with worst compatibility
  std::vector<RefCountedVertexTrack>::iterator iWorst = vtxTracks.end();
  float worseChi2 = 0.;
  for (std::vector<RefCountedVertexTrack>::iterator itr = vtxTracks.begin(); itr != vtxTracks.end(); itr++) {
    CachingVertex<5> newV = theUpdator->remove(vtx, *itr);
    if (!newV.isValid())
      return itr;
    std::pair<bool, double> result = theEstimator->estimate(newV, *itr);
    if (!result.first)
      return itr;
    float chi2 = result.second;

    // compute number of degrees of freedom
    if (chi2 > 0.) {
      // we want to keep negative chi squares, and avoid calling
      // ChiSquaredProbability with a negative chi2.
      int ndf = 2;
      if (vtx.tracks().size() == 2)
        ndf = 1;

      float prob = ChiSquaredProbability(chi2, ndf);
      if (prob < cut && chi2 >= worseChi2) {
        // small inconsistency: sorting on chi2, not on chi2 probability
        // because large chi2 are not rounded off while small probabilities
        // are rounded off to 0....
        // should not matter since at a given iteration
        // all track chi2 increments have the same ndf
        iWorst = itr;
        worseChi2 = chi2;
      }
    }
  }

  return iWorst;
}