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\begin{itemize}  \item Renormalisation group good for things with structure, where correlations between sites are important. Could be good for CLUSTERING investigation, especially if I can write down a Hamiltonian for the whole system composed of other particles (will certainly have to simplify this a lot!).  \item In Langevin analysis (e.g. \citet{1975JFM....72..499H}) we define inertia and friction tensors $\mathbf{m}$ and $\mathbf\zeta$, which act on the derivative of the system's state vector $\mathbf{\dot x}$. What does it mean when these are symmetrical? When What does it mean when  they are diagonal? \begin{itemize}   \item Apparently in regimes far from equilibrium, $\mathbf\zeta$ stops being symmetrical.   \end{itemize}  \end{itemize}