用于无约束优化的鲍威尔优化方法，

程序中参数解释如下：//P:存放设计变量

//XI：存放两个线性无关的向量

//N：含有N各元素的一维实型数组，用于存储设计变量

//NP:整形变量，用于存储P与xi的维数

//FTOL：迭代精度

//FRET：输出参数，存放目标函数在找到的近似极小值点处的值

//ITER:迭代次数-For unconstrained optimization of the Powell optimization methods, procedures explained in the following parameters:// P: store design variables// XI: storing two linearly independent vector// N: contains N elements of the one-dimensional real array, design variables used to store// NP: plastic variables, used to store P and xi dimension// FTOL: iterative precision// FRET: output parameters, storage of the objective function to find the approximate minimum point value// ITER: number of iterations