Notes from Feb. 7th, 2012 Tracking Discussion with Hall-B

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The following are notes from a discussion with some Hall-B folks on charged particle tracking that took place on Feb. 7th, 2012. These were sent to Volker and Eugene on Feb. 15th.

Hi All,

  I wanted to summarize our tracking discussion from Tuesday since I
feel it addresses the topic of sharing tracking software between halls B
and D. Something we were asked to meet and discuss by Rolf.

Please have a look at the summary below and send me any corrections
you may have. My intent is to forward this to Eugene and Volker once there is

  Attending: Maurizio U., Veronique Z., Dennis W., Mac M., Mark I.,
Simon T., David L., Dave H., Vardan G., Ken H.

CLAS12 has some existing tracking code, but Maurizio and Veronique are
endeavoring to construct a new package that would allow them to more
easily modify and maintain it.

Maurizio had previously contacted David and Simon to ask about code
Hall-D used for helical fits to see if it would be appropriate for
CLAS12. Prior to the meeting Maurizio and Veronique were able to take a
look at the two algorithms currently deployed in the Hall-D tracking
code. Some discussion was had about details of how the helical fits were
done (two stages, each fit to a a set of 2-D points and each yielding 2
parameters for a total of 4 fit parameters). The code for this was
fairly general and could likely be adopted with minimal modifications
for CLAS12.

The subject of sharing code directly was discussed briefly. Hall-B was
interested in possibly developing a package with the general use
utilities that both hall's tracking codes would need. Hall-D felt that
in their experience, it was extremely difficult to maintain generality
when developing the tracking code and it might be more efficient for
each hall to maintain their own development stream, but keep close
communication so knowledge and algorithms could be shared easily. Hall-B
will move forward with development of a set of general use tracking
utilities while developing their software. Hall-D may refactor its code
in the future to adopt these generic tools at a point when it seems
appropriate to do so.

 Mac suggested that we try and look for common terminology and, wherever
possible, use similar configuration parameters for both tracking
packages. This would provide a level of continuity between the two
halls, that might make communication and comparison easier.

Hall-D went on to describe some other details of how the tracking was
done in their code. This touched on the following areas:

- How candidates are formed and how they are linked between the CDC and
FDC detectors
- If, when and how clones and ghosts are handled
- Mechanism for hit selection is done
- Kalman Filter
- SIMD instructions and linear algebra packages
- Hough transforms and Riemann fits

Maurizio and Veronique were going to get started by trying to implement
the Hall-D helical fitter  and would stay in close contact with Simon
and David as the development progressed.