witnesses, that is witnesses whose expectation value vanishes on at least one product
vector. Any weakly optimal entanglement witness can be written as the form of $
W^{wopt}=\sigma-c_ {\sigma}^{max} I $, where $ c_ {\sigma}^{max} $ is a non-negative
number and $ I $ is the identity matrix. We show the relation between the weakly optimal
witness $ W^{wopt} $ and the eigenvalues of the separable states $\sigma $. Further we …