Modified HDDM model to hold intermediary states

[David Lawrence <davidl@jlab.org>]

Hi Folks,

    I just committed a change to the HDDM data model to the repository 
so that intermediary states can be stored along with the final state 
particles in the output of hdgeant. This was discussed at the last few 
software meetings. Corresponding changes were made to hdgeant, 
genr8_2hddm, DMCThrown, ... as well as pythiagen. Currently, only 
pythiagen puts anything useful in the new fields which are:

pdgtype
id
parentid
mech

The pdgtype uses the MC numbering scheme from the PDG (which is what 
pythia uses internally). The id and parent id allow the parent, child 
relationship to be specified. The mech value is passed over from pythia 
and presumably has something to do with the production mechanism of the 
particle.

NOTE: If you update you source now, you will have a data model that is 
inconsistent with any simulation files you may have lying around. You 
will still be able to read the old files, but you will not be able to 
access the "thrown" values since that is the part of HDDM that was 
changed. I recommend only updating when you are ready to generate new 
simulation files since it may save yourself a little headache.

If you have any questions or problems, let me know.

Regards,
-David

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  David Lawrence Ph.D.
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