  We show how the steady-state solution of the Smoluchowski (Fokker-Planck)
equation for a color reaction-counterdiffusion problem, together with
equilibrium trajectory information (e.g., from molecular simulations or
confocal microscopy experiments), can be used to determine position-dependent
or pair diffusivity profiles for condensed phases directly without the need for
Bayesian inference, likelihood maximization, or the analysis of time-dependent
data.
