115 add an option to check if a track is a descendant of another track in the trackmap

include/SimCore/TrackMap.h

@@ -41,6 +41,12 @@ class TrackMap {
     return ancestry_.find(track->GetTrackID()) != ancestry_.end();
   }
 
+  /**
+   * Check if the track with the given ID is a descendant of the track with
+   * the given ancestor ID up to a given depth.
+   */
+  bool isDescendant(int trackID, int ancestorID, int maximum_depth) const;
+
   /**
    * Find a trajectory's nearest parent that is incident on the calorimeter
    * region. We assume that the primary particles have a parent ID of 0.

src/SimCore/TrackMap.cxx

@@ -6,6 +6,26 @@
 
 namespace simcore {
 
+bool TrackMap::isDescendant(int trackID, int ancestorID,
+                            int maximum_depth) const {
+  int current_depth{0};
+  int current_track{trackID};
+  // Walk the tree until we either no longer have a parent or we reach the
+  // desired depth
+  while (current_depth < maximum_depth &&
+         (ancestry_.find(current_track) != ancestry_.end())) {
+    // See if we have encountered the parent of the current track
+    //
+    // operator[] is not const, so we need to use at()
+    current_track = ancestry_.at(current_track).first;
+    if (current_track == ancestorID) {
+      // If one of the parents is the track of interest, we are done!
+      return true;
+    }
+    current_depth++;
+  }
+  return false;
+}
 void TrackMap::insert(const G4Track* track) {
   ancestry_[track->GetTrackID()] =
       std::make_pair(track->GetParentID(), isInCalorimeterRegion(track));