PE.m computes efficiently empirical permutation entropy. PEeq.m computes efficiently empirical permutation entropy for the case of modified ordinal patterns. The methods are based on precomputing values of successive ordinal patterns of order d, using the fact that they are "overlapped" in d points, and on precomputing successive values of the permutation entropy related to "overlapping" successive time-windows .
1 Unakafova, V. A., & Keller, K. (2013). Efficiently Measuring Complexity on the Basis of Real-World Data. Entropy, 15(10), 4392-4415.