“…Therefore, the membership function in this paper is a natural extension of Tanaka et al (2000), Guo et al (2002), Tanaka and Guo (1999), Zhang and Wang (2005), Zhang (2007), Carlsson et al (2002). The membership function f j (u), u ∈ R, whose value is interpreted as the degree of possibility of the statement that "r j (u) will be the rate of return on the ith asset" The detailed statements can be found in Inuiguchi and Tanino (2000), Tanaka et al (2000), Guo et al (2002), Tanaka and Guo (1999), Zhang and Wang (2005), Zhang (2007), Zhang et al (2007), Carlsson et al (2002).…”