FR共轭梯度算法求极小值。y为给定函数，x为函数变量，x0为搜索起始点 返回值fm为极小值，xm为极小值点-FR conjugate gradient algorithm for the minimum. y for a given function, x as a function of variables, x0 the starting point for the search to return to the value of fm for the minimum, xm for t