Importing Old Issues - incorporate the background component as an argument to calc_stat_func

[anetasie]

This is an issue sent by a user to the CXC helpdesk pointing out the limitations of the calc_stat_function.
This issue limits the user_stat functionality. There is no workaround..

"So I'm trying to define a w-statistic function for use in fitting some data, and I'm trying to follow the examples and documentation at http: //cxc.harvard.edu/sherpa/faq/user_stat.html and
http: //cxc.harvard.edu/sherpa/ahelp/load_user_stat.html, and the definition of the w-statistic at
http: //heasarc.nasa.gov/xanadu/xspec/manual/XSappendixStatistics.html (at
the end of the second cstat section).

My question is, how does a statistic-calculating function gain access to the
backgrounds from the pha file? According to the documentation the function
definition should look like

---

def calc_stat_func(data, model, staterror=None, syserror=None, weight=None):

---

and that doesn't have a "background" argument."

[DougBurke]

This is addressed in #90