Divergent or convergent transformation process under three variables. (a) Initial distance dis and relaxation time τ with v^o = 1.3 m/s. (b) Initial distance dis and desired velocity v^o with τ = 0.5 s. (c) Relaxation time τ and desired velocity v^o with dis = 0.1 m. Because the value of f f has no qualitative influence on the convergence, f f is fixed at 10⁻³. The dotted lines are boundaries from convergence analysis.