I use Semantic in Emacs to do the auto compeletion job. But it cannot parse the Eigen header files without suffix '.h', such as "Dense". I report this problem to CEDET dev group and they suggest me to add a mode cookie in the header file, for example :

// Components for manipulating sequences of characters -*- C++ -*-

This sentence can be found in the C++ header <string> and the method really works(many thanks to Eric M. Ludlam and David Engster for their solution).

I find 33 header files without suffix '.h' under the "Eigen/Eigen" folder, but I don't konw whter there are other headers in this style or not...

Maybe the mode cookie can be added to all the headers without suffix '.h' in the future version.