Based on a trigonometric function, an effective entropy measure for intuitionistic fuzzy sets is proposed. The
entropy measure reflects not only the difference between the membership degree and the nonmembership degree, but also the
hesitancy degree. Then two intuitionistic fuzzy entropy formulas proposed by former references are discussed and compared
with the proposed formula. Numerical examples are given to show that the proposed entropy measure can measure the
fuzziness and intuitionism of intuitionistic fuzzy sets.