Before revision:  We show that if the number of  workers is n, and the runtime of each subtask has an exponential tail, the optimal coded matrix multiplication is \Theta(\log n) times faster than the uncoded matrix multiplication.
After revision:  We show that if the number of homogeneous workers is n, and the runtime of each subtask has an exponential tail, the optimal coded matrix multiplication is \Theta(\log n) times faster than the uncoded matrix multiplication.