On Rationality of Nonnegative Matrix Factorization by Chistikov, D, Kiefer, S, Marusic, I, Shirmohammadi, M, Worrell, J

“…NMF has a wide variety of applications, in- cluding bioinformatics, chemometrics, communication com- plexity, machine learning, polyhedral combinatorics, among many others. A longstanding open question, posed by Cohen and Rothblum in 1993, is whether every rational matrix M has an NMF with minimal d whose factors W and H are also rational. …”