ITS: add selections on tracks sharing clusters

DataFormats/Detectors/ITSMFT/ITS/include/DataFormatsITS/TrackITS.h

@@ -194,6 +194,12 @@ class TrackITSExt : public TrackITS
 
   GPUhdi() const int& getClusterIndex(int lr) const { return mIndex[lr]; }
 
+  GPUh() const int& getFirstLayerClusterIndex() const
+  {
+    int firstLayer = getFirstClusterLayer();
+    return getClusterIndex(firstLayer);
+  }
+
   GPUhdi() void setExternalClusterIndex(int layer, int idx, bool newCluster = false)
   {
     if (newCluster) {

Detectors/ITSMFT/ITS/tracking/include/ITStracking/Configuration.h

@@ -98,6 +98,11 @@ struct TrackingParameters {
   bool PrintMemory = false; // print allocator usage in epilog report
   size_t MaxMemory = std::numeric_limits<size_t>::max();
   bool DropTFUponFailure = false;
+
+  // Selections on tracks sharing clusters
+  float SharedClusterMaxDeltaPhi = 0.05f; // For tracks sharing clusters, maximum allowed delta phi at the cluster position
+  float SharedClusterMaxDeltaEta = 0.03f; // For tracks sharing clusters, maximum allowed delta eta at the cluster position
+  bool SharedClusterOppositeSign = false; // For tracks sharing clusters, require opposite sign of the tracklets
 };
 
 struct VertexingParameters {

Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackerTraits.h

@@ -58,6 +58,8 @@ class TrackerTraits
   void acceptTracks(int iteration, bounded_vector<TrackITSExt>& tracks, bounded_vector<bounded_vector<int>>& firstClusters, bounded_vector<bounded_vector<int>>& sharedFirstClusters);
   void markTracks(int iteration, bounded_vector<bounded_vector<int>>& sharedFirstClusters);
 
+  bool areTracksSelected(int iteration, const TrackITSExt& t1, const TrackITSExt& t2);
+
   void updateTrackingParameters(const std::vector<TrackingParameters>& trkPars)
   {
     mTrkParams = trkPars;

Detectors/ITSMFT/ITS/tracking/include/ITStracking/TrackingConfigParam.h

@@ -104,6 +104,11 @@ struct TrackerParamConfig : public o2::conf::ConfigurableParamHelper<TrackerPara
   bool fataliseUponFailure = true;       // granular management of the fatalisation in async mode
   bool allowSharingFirstCluster = false; // allow first cluster sharing among tracks
 
+  // Selections on tracks sharing clusters
+  float sharedClusterMaxDeltaPhi = 0.05f; // Maximum allowed delta phi at the cluster position
+  float sharedClusterMaxDeltaEta = 0.03f; // Maximum allowed delta eta at the cluster position
+  bool sharedClusterOppositeSign = false; // Require opposite sign of the tracklets
+
   O2ParamDef(TrackerParamConfig, "ITSCATrackerParam");
 };
 

Detectors/ITSMFT/ITS/tracking/src/Configuration.cxx

@@ -204,6 +204,9 @@ std::vector<TrackingParameters> TrackingMode::getTrackingParameters(TrackingMode
     p.SaveTimeBenchmarks = tc.saveTimeBenchmarks;
     p.FataliseUponFailure = tc.fataliseUponFailure;
     p.AllowSharingFirstCluster = tc.allowSharingFirstCluster;
+    p.SharedClusterMaxDeltaPhi = tc.sharedClusterMaxDeltaPhi;
+    p.SharedClusterMaxDeltaEta = tc.sharedClusterMaxDeltaEta;
+    p.SharedClusterOppositeSign = tc.sharedClusterOppositeSign;
     const auto iter = &p - trackParams.data();
     if (iter < constants::MaxIter) {
       p.MaxHoles = tc.maxHolesIter[iter];

Detectors/ITSMFT/ITS/tracking/src/TrackerTraits.cxx

@@ -876,23 +876,52 @@ void TrackerTraits<NLayers>::markTracks(int iteration, bounded_vector<bounded_ve
       std::sort(sharedFirstClusters[iLayer].begin(), sharedFirstClusters[iLayer].end());
     }
 
-    for (auto& track : mTimeFrame->getTracks()) {
-      int firstLayer{mTrkParams[iteration].NLayers}, firstCluster{constants::UnusedIndex};
-      for (int iLayer{0}; iLayer < mTrkParams[iteration].NLayers; ++iLayer) {
-        if (track.getClusterIndex(iLayer) == constants::UnusedIndex) {
-          continue;
-        }
-        firstLayer = iLayer;
-        firstCluster = track.getClusterIndex(iLayer);
-        break;
-      }
+    auto& tracks = mTimeFrame->getTracks();
+    std::sort(tracks.begin(), tracks.end(), [](const auto& t1, const auto& t2) {
+      return t1.getFirstLayerClusterIndex() < t2.getFirstLayerClusterIndex();
+    });
+
+    for (int i{0}; i < static_cast<int>(tracks.size()); ++i) {
+      auto& track = tracks[i];
+      int firstLayer{track.getFirstClusterLayer()}, firstCluster{track.getFirstLayerClusterIndex()};
       if (std::binary_search(sharedFirstClusters[firstLayer].begin(), sharedFirstClusters[firstLayer].end(), firstCluster)) {
-        track.setSharedClusters();
+        int j = i + 1;
+        while (j < static_cast<int>(tracks.size()) && tracks[j].getFirstLayerClusterIndex() == firstCluster) {
+          auto& track2 = tracks[j];
+          if (areTracksSelected(iteration, track, track2)) {
+            for (int iLayer{track.getFirstClusterLayer()}; iLayer < track.getFirstClusterLayer() + track.getNClusters(); ++iLayer) {
+            }
+            for (int iLayer{track2.getFirstClusterLayer()}; iLayer < track2.getFirstClusterLayer() + track2.getNClusters(); ++iLayer) {
+            }
+            track.setSharedClusters();
+            track2.setSharedClusters();
+          }
+          ++j;
+        }
       }
     }
   }
 }
 
+template <int NLayers>
+bool TrackerTraits<NLayers>::areTracksSelected(int iteration, const TrackITSExt& t1, const TrackITSExt& t2)
+{
+  const auto t1FirstLayer{t1.getFirstClusterLayer()}, t2FirstLayer{t2.getFirstClusterLayer()};
+  if (mTimeFrame->getClusterROF(t1FirstLayer, t1.getClusterIndex(t1FirstLayer)) != mTimeFrame->getClusterROF(t2FirstLayer, t2.getClusterIndex(t2FirstLayer))) {
+    return false;
+  }
+  if (o2::math_utils::detail::deltaPhiSmall(t1.getPhi(), t2.getPhi()) > mTrkParams[iteration].SharedClusterMaxDeltaPhi) {
+    return false;
+  }
+  if (std::abs(t1.getEta() - t2.getEta()) > mTrkParams[iteration].SharedClusterMaxDeltaEta) {
+    return false;
+  }
+  if (mTrkParams[iteration].SharedClusterOppositeSign && t1.getSign() == t2.getSign()) {
+    return false;
+  }
+  return true;
+}
+
 template <int NLayers>
 void TrackerTraits<NLayers>::setBz(float bz)
 {