Eigen is primarily MPL2 licensed. See COPYING.MPL2 and these links:&#xA;  http://www.mozilla.org/MPL/2.0/&#xA;  http://www.mozilla.org/MPL/2.0/FAQ.html&#xA;&#xA;Some files contain third-party code under BSD or LGPL licenses, whence the other&#xA;COPYING.* files here.&#xA;&#xA;All the LGPL code is either LGPL 2.1-only, or LGPL 2.1-or-later.&#xA;For this reason, the COPYING.LGPL file contains the LGPL 2.1 text.&#xA;&#xA;If you want to guarantee that the Eigen code that you are #including is licensed&#xA;under the MPL2 and possibly more permissive licenses (like BSD), #define this&#xA;preprocessor symbol:&#xA;  EIGEN_MPL2_ONLY&#xA;For example, with most compilers, you could add this to your project CXXFLAGS:&#xA;  -DEIGEN_MPL2_ONLY&#xA;This will cause a compilation error to be generated if you #include any code that is&#xA;LGPL licensed.&#xA;