\item calculate: $r_{ik}$, $r_{ik}^2$
\item IF $r_{ik} > S_{ik}$ THEN CONTINUE
\item calculate: $\theta_{ijk}$, $\cos(\theta_{ijk})$,
\item calculate: $r_{ik}$, $r_{ik}^2$
\item IF $r_{ik} > S_{ik}$ THEN CONTINUE
\item calculate: $\theta_{ijk}$, $\cos(\theta_{ijk})$,