Eigen3 is a powerful and versatile C++ library used for linear algebra, making it a great choice for scientific computing, 3D graphics, or any application involving matrices and vectors. This guide will walk you through how to install Eigen3, set up a simple project using CMake, and write a basic Eigen3 example in C++.

Table of Contents

  1. Installing Eigen3
  2. Setting Up CMake
  3. Creating a Simple Eigen3 Example

By the end of this post, you’ll have a small project that compiles and runs a basic example using Eigen3. This post should take about 10 minutes to read and follow along.

1. Installing Eigen3

Before diving into coding, you need to have Eigen3 installed on your system. Here’s how to do it on different platforms:

Ubuntu 18.04

On Ubuntu, installing Eigen3 is straightforward with the following command:

sudo apt install libeigen3-dev -y

Arch Linux

If you’re using Arch Linux, you can install it via pacman:

sudo pacman -S eigen --noconfirm

Windows using vcpkg

For Windows users, we recommend using vcpkg to install Eigen3:

vcpkg install eigen3

Once installed, you’re ready to set up your project using CMake.

2. Setting Up CMake

Now that Eigen3 is installed, let’s create a simple project structure and set up CMake to use Eigen3.

Step 1: Create the Project Directory

Start by creating a new project folder and its subdirectories:

mkdir eigen3_tutorial/{src,build} -p
cd eigen3_tutorial/src
touch CMakeLists.txt main.cpp

This will create a folder structure with a src directory for your source code and a build directory where CMake will generate the necessary files for compiling your project.

Step 2: Create the CMakeLists.txt

In the src directory, open the CMakeLists.txt file and add the following content:

cmake_minimum_required(VERSION 3.9)
project(eigen3_tutorial CXX)

find_package(Eigen3 REQUIRED)

add_executable(
  eigen3_tutorial
  main.cpp
)

target_link_libraries(
  eigen3_tutorial
  PRIVATE
  Eigen3::Eigen
)

This CMake configuration will find the Eigen3 library and link it to your project. It ensures that Eigen3 is properly included in your build process.

Step 3: Create the main.cpp

Now let’s create a simple main.cpp file:

int main(int argc, char* argv[]) {
  return 0;
}

This empty main function serves as a placeholder. Next, we’ll add a small example using Eigen3.

3. Creating a Simple Eigen3 Example

Let’s modify the main.cpp to include a basic example with Eigen3. In this example, we’ll create a vector and print its transpose to the console.

Update the main.cpp file with the following code:

#include <iostream>

#include <Eigen/Core>

int main(int argc, char* argv[]) {
  Eigen::Vector3d vec3;
  vec3 << 1, 2, 3;

  std::cout << vec3.transpose() << '\n';
  return 0;
}

Explanation

Step 4: Build and Run the Project

Navigate to the build directory and run the following commands to compile and run the project:

cd ../build
cmake ../src
make
./eigen3_tutorial

If everything is set up correctly, you should see the following output:

1 2 3

Conclusion

You’ve just installed Eigen3, set up a simple CMake project, and written a basic example in C++ using Eigen3. Eigen3 is incredibly powerful, and this guide serves as a foundation to get you started. You can now explore more complex operations and use Eigen3 in your projects.