Furthermore, the random baseline RANDOMM2 tests a hypothesis that joint training might be just clustering M 3 and M 1 here, to the extent that M 3 and M 1 are so close that even a random M 2 can give the correct answer; but as it turns out, JOINT+COMP largely outperforms RANDOMM2, excluding this possibility.
joint training performs better not simply because it clusters relation matrices; it learns compositions indeed.