  We show a simple semidefinite program whose optimal value is equal to the
maximum probability of perfectly distinguishing orthogonal maximally entangled
states using any PPT measurement (a measurement whose operators are positive
under partial transpose). When the states to be distinguished are given by the
tensor product of Bell states, the semidefinite program simplifies to a linear
program. In [Phys. Rev. Lett. 109, 020506 (2012) -- arXiv:1107.3224v1], Yu,
Duan and Ying exhibit a set of 4 maximally entangled states in $C^4 \otimes
C^4$, which is distinguishable by any PPT measurement only with probability
strictly less than 1. Using semidefinite programming, we show a tight bound of
7/8 on this probability (3/4 for the case of unambiguous PPT measurements). We
generalize this result by demonstrating a simple construction of a set of k
states in $C^k \otimes C^k$ with the same property, for any k that is a power
of 2. Finally, by running numerical experiments, we obtain some non-trivial
results about the PPT-distinguishability of certain interesting sets of
generalized Bell states in $C^5 \otimes C^5$ and $C^6 \otimes C^6$.
