Multiple Time Step Method

A `distance class' is defined as follows: Let $\{R_{0} = 0,R_{1},\ldots ,R_{n} \}$ be a set of radii with R_j<R_j+1 for all $j=0,1,\ldots ,n-1$ . Then the set of particles k with positions $\vec{r}_{k}$ satisfying the condition $R_{j}\leq \vert\vec{r}_{i}-\vec{r}_{k}\vert<R_{j+1}$