Eigen中是否有运算符或函数将向量或矩阵的元素读取为单独的变量？例如，我想象逗号初始化程序的相反过程：
Eigen::Vector5d v;
v << a,b,c,d,e;
// ... do something with v ...
v >> a,e; // is there a way to do what I'm trying to do here,in one simple line?
我所知道的唯一方法是使用5层衬垫：
a = v(0);
b = v(1);
c = v(2);
d = v(3);
e = v(4);