Vertex finding is for associating certain tracks to a potential (either primary or secondary) vertex. It is one amongst the difficult tasks in the tracking reconstruction chain. General vertex finding is eventually expected. It is also desirable (and less difficult) if some vertex finding algorithms are only suitable for certain physics channels.
Vertex finding code will read tracks from bank TRAK, then modify the column (1), i.e. to give a vertex ID to a track as IDTR = IDV*10000 + IDT .