Convention for partial static structure factor

[mphoward]

The documentation for StaticStructureFactorDirect says that the total structure factor is the number-weighted double sum of partial structure factors and that the normalization used is based on the Faber-Ziman formalism, which would be consistent with this equation. However, the example shows that the total structure factor is the double sum of partial structure factors (by direct comparison).

I read the discussion in #1313 with the OVITO developers, and I also read their documentation. I also read the source code for StaticStructureFactorDirect. Given the behavior in the example, it seems that freud is following the same convention as OVITO and not the Faber-Ziman convention? If yes, I would be happy to open a PR with small doc fixes to this effect.

[DomFijan]

The documentation has been updated since freud 3.1. to reflect the discussion in #1313 (see #1314 and glotzerlab/freud-examples#83). Is this something along the lines of what you had in mind? If we can improve upon this a PR would be welcome.

[mphoward]

Yes! Sorry, I must have pinned my documentation to the version I installed while debugging, and I didn’t realize it was out of date. The updated documentation clarifies perfectly.