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 =

" << a + b << std::endl;

  std::cout << "a - b =

" << a - b << std::endl;

  std::cout << "Doing a += b;" << std::endl;

  a += b;

  std::cout << "Now a =

" << a << std::endl;

  Vector3d v(1,2,3);

  Vector3d w(1,0,0);

  std::cout << "-v + w - v =

" << -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?