Eigen is primarily licensed under the Mozilla Public License 2.0.
See LICENSE, COPYING.MPL2, and these links:
  https://www.mozilla.org/MPL/2.0/
  https://www.mozilla.org/MPL/2.0/FAQ.html

Some files contain third-party code under permissive or otherwise
MPL2-compatible licenses, hence the other COPYING.* files here. These
include Apache-2.0, BSD-style notices, the MINPACK license, and the MORSE
CMake module BSD-style notice in cmake/MORSE-Copyright.txt.

Note that some optional external dependencies (e.g. FFTW, MPFR C++)
are distributed under different licenses, including the GPL. Refer to
the individual source files and their respective COPYING files for
details.