Appropriate mesh sizes for the two-dimensional problem First, in order to assess the size of the problem and computational requirements, we need to clarify how fine the grid of s-values and f r -values needs to be in order to fully extract all information from a typical set of sedimentation velocity data. Let us consider as an example the experimental data from a preparation of IgG molecules sedimenting at 45,000 rpm, as shown in Fig. 1a . It is useful to start the analysis with a one-dimensional sedimentation coefficient distribution analysis c(s), since the sedimentation coefficients are the experimentally best determined quantities. c(s) eliminates the shape dimension by using hydrodynamic scaling laws such as the traditional s * M 2/3 law for globular particles (Schuck 2000) , theoretical models for wormlike chains (Yamakawa and Fujii 1973) or any user-defined exponential scaling laws for polymers (Pavlov et al. 2009 ). For the given data we can determine from the c(s) analysis (not shown) that s-values from 0.1 to 15 S will be sufficient to describe all sedimenting species. Equidistant discretizations with S = 100 or S = 200 lead to statistically indistinguishable quality of fit, as measured by F-statistics (Bevington and Robinson 1992; Straume and Johnson 1992) , and therefore we preliminarily conclude that S = 100 will be a reasonable choice.