  In this paper we present the quantity, which is an entanglement parameter.
Its origin is very intriguing, because its construction is motivated by
separability criteria based on uncertainty relation. We show that this quantity
is asymptotically continuous. We also find the lower and upper bounds for it.
Our entanglement parameter has the same feature as the coherent information:
both can be negative.
  There are also some classes of states for which these quantities coincide
with each other.
