fatal error: 'eigen3/Eigen/Dense' file not found

Question

I tried to use eigen in mac. After I installing it I run a demo from its' main page.The code is as follows:

#include <iostream>
#include <eigen3/Eigen/Dense>
using Eigen::MatrixXd;
int main()
{
 MatrixXd m(2,2);
 m(0,0) = 3;
 m(1,0) = 2.5;
 m(0,1) = -1;
 m(1,1) = m(1,0) + m(0,1);
 std::cout << m << std::endl;
}

And I write following code in terminal:

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

It turns out like that:

aaa.cpp:2:10: fatal error: 'eigen3/Eigen/Dense' file not found

However I can run this code perfectly in Xcode. Who can help me to fix it?

Answer 1

Change your include line to

#include <Eigen/Dense>

or

#include <Eigen/Core>

and your command line to

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

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