external calls to sasmodels needing beta(Q)

[richardh]

Do we need to consider how other codes will be able to call sasmodels in such as way as to get beta(Q) and other options in the calculation of I(Q)?

[tcbennun]

External code can use several methods to run sasmodels, but in the beta_approx branch, the SasviewModel class has an API change in place allowing access to intermediate results from the P(Q)S(Q) calculation.

SasviewModel.calculate_Iq now returns both I(Q) and a callable; the callable is used to generate a dict of intermediate results. beta(Q) is one of those results, if beta approximation is turned on. If the model in question is not a product model, the callable returns an empty dict.

This is a breaking change for any existing calls to calculate_Iq, so if/when this is introduced into master, it must be under a new major version number (I recommend).

[pkienzle]

For scripts that use the sasview model wrapper (if any), the first release of beta approximation will be in sasmodels 1.0, so it will be in a new major revision.

Closing this as dup of #491.