The four parameter combinations

In model-free analysis four different combinations of parameters can be optimised, each of which requires a different approach to the construction of the chi-squared value, gradient, and Hessian. These categories depend on whether the model-free parameter set $\mathfrak{F}$, the diffusion tensor parameter set $\mathfrak{D}$, or both sets are simultaneously optimised. The addition of the local τ_m parameter to the model-free set $\mathfrak{F}$ creates a fourth parameter combination.