“…Similarly, the object set of low cost:{5,10,11,12,13}, the object set of medium cost:{1, 4,6,8,9,15,16,17,18,20,22,24,25} and the object set of high cost:{2,3,7,14,19,21,23} can be obtained (Figure 2 in Appendix). Correspondingly, the formulas were divided into three categories: low cost (W1), medium cost (W2) and high cost (W3).…”