Eventually, we terminate the algorithm after 50 iterations, since the MSE value seems to hardly decrease after the 40 th iteration. The effect of the two principles can be merged to improve efficiency of surrogate generation for PSA. As shown in Figure , if equally sampling without classifier is applied, the time spent on surrogate generation for PSA is 3.9e6 s, which can be reduced by 88% if the two principles apply (4.8e5 s). A separate dataset was used to test the performance of the iteratively refined surrogate for PSA.