How to check the version number of Eigen C++ template library?

This answer is only a summary from the comments above:

• At compile-time you have EIGEN_WORLD_VERSION, EIGEN_MAJOR_VERSION
  and EIGEN_MINOR_VERSION, you can easily embed this information in
  your application.

• 3.1.91 sounds like a beta version of 3.2.

• The version number macros are defined in Macros.h located at
  \Eigen\src\Core\util\.