Eigen installation seemed to work, but I still can't make eigen work

Question

I am trying to install eigen, but I don't seem to get it to work.

I did:

sudo apt-get install libeigen3-dev

and everything seems fine, after

dpkg -p libeigen3-dev

I get:

Package: libeigen3-dev
Priority: extra
Section: libdevel
Installed-Size: 3718
Maintainer: Ubuntu Developers <[email protected]>
Architecture: all
Source: eigen3
Version: 3.2.0-4
Depends: pkg-config
Suggests: libeigen3-doc
Size: 698062
Description: lightweight C++ template library for linear algebra
 Eigen 3 is a lightweight C++ template library for vector and matrix math,
 a.k.a. linear algebra.
 .
 Unlike most other linear algebra libraries, Eigen 3 focuses on the simple
 mathematical needs of applications: games and other OpenGL apps, spreadsheets
 and other office apps, etc. Eigen 3 is dedicated to providing optimal speed
 with GCC. A lot of improvements since 2-nd version of Eigen.
Original-Maintainer: Debian Science Maintainers <[email protected]>
Homepage: http://eigen.tuxfamily.org

Everything looked fine to me. However, when I try to compile the basic code (given in the tutorial):

first_eigen.cpp

#include <iostream>
#include <Eigen/Dense>
using namespace Eigen;
int main()
{
  Matrix2d a;
  a << 1, 2,
  3, 4;
  MatrixXd b(2,2);
  b << 2, 3,
  1, 4;
  std::cout << "a + b =\n" << a + b << std::endl;
  std::cout << "a - b =\n" << a - b << std::endl;
  std::cout << "Doing a += b;" << std::endl;
  a += b;
  std::cout << "Now a =\n" << a << std::endl;
  Vector3d v(1,2,3);
  Vector3d w(1,0,0);
  std::cout << "-v + w - v =\n" << -v + w - v << std::endl;
}

I run it in the shell like this:

g++ -std=c++11 first_eigen.cpp -o my_exec

I get the following error:

first_eigen.cpp:2:23: fatal error: Eigen/Dense: No such file or directory
 #include <Eigen/Dense>
                       ^
compilation terminated.

So it looks like eigen was not installed. What am I missing?

Answer 1

The eigen3 header files go in a subdirectory /usr/include/eigen3 e.g.

/usr/include/eigen3/Eigen/Array
/usr/include/eigen3/Eigen/Cholesky
/usr/include/eigen3/Eigen/CholmodSupport
/usr/include/eigen3/Eigen/Core
/usr/include/eigen3/Eigen/Dense
/usr/include/eigen3/Eigen/Eigen

so you will need to specify the additional include path on your compiler command line, for example

g++ -std=c++11 -I/usr/include/eigen3 first_eigen.cpp -o my_exec

Alternatively (and possibly more portably), you can use the pkg-config database to automate the inclusion, i.e.

g++ -std=c++11 `pkg-config --cflags eigen3` first_eigen.cpp -o my_exec

Answer 2

Change the include to

#include <eigen3/Eigen/Dense>

Answer 3

Pls. look if you have a folder named "Eigen" in /usr/include.

I don't know eigen and the installation routine. But very often the dev includes are named with a version.

If you have a "Eigen3" folder in your /usr/include directory, you should change your code to:

#include <Eigen3/Dense>