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( a )
( b ) Figure 6. The Gantt charts of Job16, ( a , b ) are Gantt charts of the first and second operation of Job16 respectively; the makespan and energy cost of NSGA-II, SPEA2, MOEA/D-MR, and IMOEA/DTL are (4.0066 × 10 4 , 3.3994 × 10 6 ), (4.0020 × 10 4 , 3.3900 × 10 6 ), (4.0029 × 10 4 , 3.4038 × 10 6 ), and (3.9960 × 10 4 , 3.3800 × 10 6 ) respectively.
Table 12 shows the average makespan and average energy cost obtained by MOEA/D- MR, NSGA-II, SPEA2, and IMOEA/DTL. Table 12 indicates that both the average makespan and average energy cost obtained by IMOEA/DTL are lower than those obtained by MOEA/D-MR, NSGA-II, and SPEA2. Therefore, IMOEA/DTL can provide the solution with lower makespan and energy cost than MOEA/D-MR, NSGA-II, and SPEA2. This study adopts a multi-objective algorithm, and a non-dominated solution set is obtained. The solutions in the non-dominated solution set have lower energy cost or makespan, but they are mutually exclusive. Decision makers can select an optimal solution on the basis of actual situations. For instance, the solution with a low makespan can be selected in the case of a heavy production task, which can improve the utilization efficiency of the workshop and ensure that the task can be completed on schedule. On the contrary, the decision-makers can choose the optimal solution with low energy cost to reduce the production cost.
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