Simulation of XPCS patterns

This program generates movies of scattering patterns of ensembles of particles. Four ensemble types are possible: a single randomly moving particle (circle) in a plane containing other fixed identical particles; an ensemble of particles for which their Brownian motion average amplitudes increases with the square root of the frame number, thus simulating a linear increase in temperature; a regular square array of particles slowly diffusing to random positions, thus simulating a crystal-to-liquid transition; and a set of randomly tumbling ellipsoids. In each case, one has the option to include (or not) a difference plot between the most recent XPCS pattern and the one previous. This is particularly insightful for the single-particle and linear-temperature-increase options.