Examples are believed to have been produced from work on the Prim-9 graphics system at Stanford Linear Accelerator. Probably related to the data cited in J. H. Friedman and J. W. Tukey, IEEE Transactions on Computing, C-23, 1974, pp. 881-889. If so, these are particle-scattering experiments, and the columns of the matrices represent some chosen set of parameters (energy, momentum, etc.) to describe the nuclear reactions.