[Primexd] Compton generators added

[Sean Dobbs]

Hi all,

I've added a generator "gen_compton_simple" to our standard
repository, based on Ilya's lowest order generator which he provided
last week (once someone merges my changes!) - sorry that it took me
awhile to free some time to implement this.  There are some command
line flags which can be set, look at "gen_compton_simple -h" for some
guidence.

I talked to Ilya about it this morning, and we have some ideas for
improvements, like modifying teh z-distribution of events (right now,
it places events based on the target definition in the geometry
description), and different beam distributions (right now it assumes
bremsstrahlung 1/E(gamma).

This program includes output to HDDM, so it can be sent through the
standard simulation & reconstruction chain.  Hopefully someone can
take a look at the output of the generator to make sure nothing is
lost in translation - I only did some brief tests.  Also, note that
there is a "gen_compton" program which relies on AmpTools (part of the
), which could also be used for initial studies.

I've started an installation of the standard simulation package at the
following location, which people can point to at JLab:
/w/halld-scifs17exp/halld2/home/sdobbs/Software/primex/halld_sim
I'll keep it updated as we merge more software in.

Cheers,
Sean