Eigen  3.4.90 (git rev a4098ac676528a83cfb73d4d26ce1b42ec05f47c)
#include <Eigen/MetisSupport>

This module defines an interface to the METIS reordering package (http://glaros.dtc.umn.edu/gkhome/views/metis). It can be used just as any other built-in method as explained in here.