[Halld-offline] hdparsim covariance matrix

[Will Levine]

Hi everyone,
I've just started working with Curits on the kinematic fitter, trying
to get it to work with hdparsim. The kinematic fitter needs a
covariance matrix for each particle, which hdparsim does not currently
provide, so I have to construct a covariance matrix based on the
parameters used to smear the particles. If this would be useful for
others, I would of course be happy to contribute my code. Currently,
I've modified hdparsim directly, so that it creates DParticles and
DPhotons with a real error matrix. If this is somehow undesirable, I
could try to do this work somewhere outside hdparsim. Thoughts?

Will