Comparison between Fuzzy and Not Fuzzy Portfolio Optimization under Downside Risk Measures

This paper presents two fuzzy portfolio selection models where the objective is to minimize the downside risk constrained so that a given expected return should be achieved. We assume that the rates of returns on securities are approximated as LR-fuzzy numbers of the same shape, and that the expected return and risk are evaluated by interval-valued means. We establish the relationship between those mean-interval definitions for a given fuzzy portfolio by using suitable ordering relations. And then we compare those with a given not fuzzy portfolio one. Finally, we formulate the portfolio selection problem as a linear program when the returns on the assets are of trapezoidal form.