Similarly,wederivethelowerboundasbelow. E(X(k)) =E(PX(k 1) W(k)) =tr((PX(k 1) W(k)) > (PX(k 1) W(k))) tr((PX(k 1)) > (PX(k 1)))σmin(W(k)(W(k)) >) =tr((PX(k 1)) > (PX(k 1)))s(k)