The figure shows that the greedy approach can scale comfortably to large data sizes, and a complete run on the entire Penn Treebank data finishes in just 1485 seconds.
the IP method does not scale well-on average, it takes 93 seconds to finish on the 24k test (versus 34 seconds for MIN-GREEDY) and on the larger PTB test data, the IP solver runs for  It is interesting to see that for the 24k dataset, the greedy strategy finds a grammar set (containing only 478 tag bigrams).