All the documentation included in the Eigen 3 distribution is in the form of .dox files. An extensive search of the internet, the Eigen website, and this forum has been inconclusive. Apparently doxygen can read them, but not display them. They are readable through a text editor without formatting. So just what is this mysterious .dox format and how are they best read?

The "make doc" command runs doxygen, which converts the .dox files and comments in the C++ source into HTML pages. The resulting output can be seen online at http://eigen.tuxfamily.org/dox-devel/ (for the development branch).

Thank you! Perhaps it would be good to add those two sentences to an Eigen README file or the INSTALL file. Just sayin.