 All the possible points ("x", "y") fall on the one-dimensional line "y = ax + b".In general when one or more of "n" random variables are exactly linearly determined by the others, if the covariance matrix exists its determinant is 0, so it is positive semi-definite but not positive definite, and the joint probability distribution is degenerate.Degeneracy can also occur even with non-zero covariance.