To add a method to the Eigen library using EIGENMATRIXBASEPLUGIN, follow these steps:

1. Create a header file (e.g., MyPlugin.h) containing the method you want to add to Eigen. The header file should include Eigen/Core and define a template struct that inherits from Eigen::MatrixBase.

2. Define the new method within the template struct. The method should take Eigen::Index rows, Eigen::Index cols, and any other necessary arguments, and return a new Eigen::Matrix.

3. Save the header file in a location that your compiler will be able to find it.

4. In your main code file, include the header file containing the new method you want to add to Eigen.

5. Set the EIGENMATRIXBASEPLUGIN preprocessor macro to the location of the header file containing your new method. For example, if your new method is defined in MyPlugin.h and is located in the same folder as your main code file, you would add the following line before including Eigen/Core:

define EIGENMATRIXBASEPLUGIN "MyPlugin.h"

1. You can now use the new method in your main code file as if it were a built-in Eigen method. For example, you could create a new matrix using the following code:

Eigen::Matrix<double, 3,="" 3=""> myMatrix = Eigen::Matrix<double, 3,="" 3="">::Random().myMethod(3, 3, someOtherArg);