Test against xpcs-baseline

[danielballan]

In CI, download the dataset generated by a LAMMPS simulation, run the implementations against it, obtained a measured coefficient of diffusion, and compare it to the known ground truth. We could define some tolerance for passing a test using pytest, or we could just track the accuracy using asv.

Code is at: https://github.com/aryabhatt/xpcs-baseline
Binary artifact is on Globus at: https://daf20b.36fe.dn.glob.us/My Drive/XPCS Sims/xpcs750k.h5

[danielballan]

A suggestion from @qzhang234, quoted from the Nikea Slack:

Take the real space pattern that produces the speckles and translates it in the real space. The decay in g2 should match the speed of translation. And if you oscillate it then the oscillation period of g2 should match that in the real space as well.

@aryabhatt Do you think it would easy to generate a second example using your xpcs-baseline code to support this suggestion?