https://www.mitpressjournals.org/doi/pdf/10.1162/neco.1993.5.2.205 (Publisher version)
Dayan, P., & Sejnowski, T. (1993). The Variance of Covariance Rules for Associative Matrix Memories and Reinforcement Learning. Neural computation, 5(2), 205-209. doi:10.1162/neco.1993.5.2.205.