§1.直和法实际工作中往往遇到因子较多、水平数又不等的试验。这时,如果把全部因子安排在一张正交表上,势必试验次数较多,要经过很长的时间才能得出结果,不能在试验过程中随时发现问题及时加以处理。直和法就是针对这类问题提出的一种有效方法,其基本思想是把试验分阶段进行,先把一部分因子和水平安排在 § 1. The direct sum method often encounters experiments with more factors and different levels. At this time, if all the factors are arranged on an orthogonal table, the number of trials will inevitably be large. It will take a long time before the results are obtained, and problems can not be discovered at any time during the trial process. The straight-hit method is an effective method proposed for this type of problem. The basic idea is to carry out experiments in phases. First, arrange some factors and levels