How to use Eigen in a C++ program?

October 3, 2023

I read the documentation of Eigen installation. As per the documentation, only header files need to be referred in your project. As shown in the screenshot below, I included the path of the Eigen in my include directories, but the program does not recognize Eigen.

Sample Code:

#include <iostream>
#include <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;
}

How do I correctly include the Eigen into my C++ project?

>Solution :

You added path/to/eigen-3.4.0/Eigen to your include path, but then you include the header Eigen/Dense, so this looks for path/to/eigen-3.4.0/Eigen/Eigen/Dense. That’s one Eigen too many.

Set the include path to path/to/eigen-3.4.0 instead.

(Don’t be tempted to modify the include to #include <Dense> instead. It might cause Eigen to be unable to find its own headers, and can also easily lead to naming conflicts.)