The new hitfinding algorithm is based on the 2-dimensional algorithm developed for STAR. An html document for the STAR code can be found here.
For each padrow:
Here, the idea of running the hitfinder in different modes comes in. If you have not yet read it, take a look at the write-up on modes now. The mode determines the level of sophistication one wants to go to in order to extract positional information (at the cost of cpu). It is not yet clear how much one gains as one goes to more sophisticated (and slower) modes.
The algorithm goes through each approximation listed below in sequence, stopping at a particular point, depending on the mode. Note that if one goes to approximation 2 (global fitting in 2D space), there is a cluster break-up step one must go through.
That is the reason for this step. If a cluster has more than Nmax hits in it (Nmax is a new hitfinder switch), then we go through an iterative procedure to break up the cluster into several smaller clusters, each with less than Nmax hits in them. This can take a lot of time. The simple algorithm is to raise the "zero-suppression" threshold by some amount (currently hardwired, soon to be implemented as a switch), and see if the mother cluster has broken into more than one cluster. Any of the resulting clusters that have more than Nmax hits need also to have the threshold-raising applied to them. It often takes several iterations of raising the threshold step-by-step to break up BIG clusters.