This is from Hobson, Riley, Bence Mathematical Methods, p 322. A spring system is described as follows (they are floating in air like molecules):
In the following equation for the potential energy, the assumption is made that displacement is much less than equilibrium position $|R_m-T_n|>>|q_m-q_n|$
The text states that the Potential Matrix is thus constructed from the above but I don't see how: Where did these numbers come from? What does each row and column represent?