将包含行更改为

#include <Eigen/Dense>

或

#include <Eigen/Core>

和您的命令行

g++ -I /usr/local/include/eigen3 aaa.cpp -o aaa

我建议您在编译包含多个指令的任何代码后，立即在命令行中至少添加 -O1 .

I recommend also adding at least -O1 to your command line, as soon as you compile any code with more than a few instructions.