In a dispersion analysis the target function f (θ) is the chi-squared equation
where i is the summation index, R2eff is the experimental relaxation data which belongs to the data set R and includes the R2eff and R1ρ values for all experiments at all magnetic field strengths, R2eff(θ) is the back calculated relaxation data belonging to the set R(θ), and σi is the experimental R2eff/R1ρ error. For standard optimisation, the summation index ranges over the relaxation data of an individual spin. However this can be changed with clustering whereby the relaxation data from a group of spin systems are optimised using a shared set of parameters.
The relax user manual (PDF), created 2016-10-28.