Eigen in Unity

Unity3d has very basic linear algebra support, for example, in Matrix4x4, there are simple multiplication functions with vectors and matrices, however, functions like inverse and eigen value are not included. Eigen is the perfect candidate of performing complicated linear algebra algorithms, for example, Singluar Value Decomposition, Sparse Matrix, Linear Eqaution Solver.

Unity Native Programming

The key idea of integrating Eigen with Unity3d is using the native programming interface of .NET. Here is another example: Native Programming in Unity. Basically, the native programming interface of unity provides a way for .NET environment to call C functions defined in built dynamic libraries.

What we will do is:

A Minimum Example

Here is a minimum example showing how to get the trace of a matrix in Eigen.

Dynamic Library using Eigen

#define EXPORT_API __declspec(dllexport)
#include <Eigen/Dense>
using namespace Eigen;
extern "C" {
  EXPORT_API float getTrace() {
    MatrixXf m = MatrixXf::Random(4,4);
    return m.trace();

Call the Function in Unity Script

using System.Collections;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using UnityEngine;

public class EigenTest : MonoBehaviour {
  public static extern float getTrace();
  void Start () {
    Debug.Log("The trace value is: " + getTrace());


The above example is the minimal to make things work. If you want to parse a Matrix4x4 to Eigen environment, please refer to Marshaling.

Eigen is perfect for native programming because it is header-only and is potentially platform independent. If you want to understand more about this workflow, please refer to Unity Native Programming.

Thanks for reading!