  In this article we continue to study the concept of entropy introduced in
[4], [15]-[17]. We calculate entropy for a wider class of finite-dimensional
operators in comparison with [15]. We also approximate the entropy of a unitary
operator on $l^2(\mathbb{N}_0)$ by the entropy of finite-dimensional operators.
Finally we calculate the entropy of several operators on $l^2(\mathbb{N}_0)$.
