This is from Hobson, Riley, Bence Mathematical Methods, p 322. A spring system is described as follows (they are floating in air like molecules):
The equilibrium positions of four equal masses M of a square with sides 2L are $R_n=\pm L_i\pm L_j$ and displacements from equilibrium are $q_n=x_ni+y_nj$. According to the text,
"The coordinates for the system are thus x1, y1, x2, . . . , y4 and the kinetic energy of matrix A is given trivially by $MI_8$ where $I_8$ is the 8x8 identity".
What does that mean? The velocity doesn't even appear. How does that relate to energy?