If say, the predicted path covers only half of the reference path (i.e., P C = 0.5), then we expect the optimal length of the predicted path to be half of the length of the reference path.
ePL is given by: LS for a predicted path P is optimal only if PL(P ) is equal to the expected optimal lengthit is penalized when the predicted path length is shorter or longer than the expected path length: (4) There is a clear parallel between the terms of CLS and SPL.