binary source and single rho value

[rpoleski]

There is an aspect of binary source models that seems a bit strange for me know, but I see that it could be "it's user's reponsibility" approach. The issue is that we can define a binary source model and provide just a single value of rho, which is then shared by both source (as a parameter without _1 or _2). Example code:

import MulensModel as mm
m = mm.ModelParameters({'t_0_1': 1, 't_0_2': 2, 't_E': 10, 'u_0_1': 0.2, 'u_0_2': 0.1, 
                        'rho': 0.01})
print(m.source_1_parameters)
print(m.source_2_parameters)

gives following output:

    t_0 (HJD)       u_0    t_E (d)     rho
      1.00000  0.200000    10.0000 0.01000
    t_0 (HJD)       u_0    t_E (d)     rho
      2.00000  0.100000    10.0000 0.01000

Is is our intention? Of course, if one provides rho_1 it applies only to the first source.
@jenniferyee What do you think? I'm bringing this up right now because similar issue appears in xallarap models.

[rpoleski]

After discussing with @jenniferyee in person: this should give an error. Similarly, ModelParameters({'t_0': 1, 't_E': 10, 'u_0_1': 0.2, 'u_0_2': 0.1}) should give an error because there should be t_0_1 and t_0_2.
For xallarap and single luminous source, the parameters should be rho or t_star, i.e., without _1.