Include <sstream> explicitly, and don't rely on the implicit include via <complex>. This implicit dependency does no longer exist in a recent llbm release (sha 78be61871704).
Eigen is a C++ template library for linear algebra: matrices, vectors, numerical solvers, and related algorithms.
For more information go to http://eigen.tuxfamily.org/.
For pull request, bug reports, and feature requests, go to https://gitlab.com/libeigen/eigen.