说明：  遗传算法 多目标优化算法，SPEA2 主要流程：1：首先初始化一个archive的集合P1，以及一个常用的population的集合P。设置P1的大小是N1，P的大小是N。初始的时候P1是空的，而P是已经初始化好的种群个体。 2：对P1进行评价，选出来里面的pareto front为1（下面用PF1来代替了）的个体，copy到P1中，如果PF1的数量大于N1的话，这个接下来再说，目前假定PF1的数量小于N1。
(Genetic algorithm, multi-objective optimization algorithm, SPEA2 Main process: 1: first, initialize a set P1 of archive and a set P of popular. Set P1 to N1 and P to n. At the beginning, P1 is empty, and P is the initialized population. 2: Evaluate P1, select the individual whose Pareto front is 1 (Pf1 is used to replace it below), copy to P1, if the number of Pf1 is greater than N1, then let's talk about it. At present, it is assumed that the number of Pf1 is less than N1.)