threed-beam-fea/ext/eigen-3.2.7/doc/snippets/ComplexEigenSolver_eigenvectors.cpp

MatrixXcf ones = MatrixXcf::Ones(3,3);
ComplexEigenSolver<MatrixXcf> ces(ones);
cout << "The first eigenvector of the 3x3 matrix of ones is:" 
     << endl << ces.eigenvectors().col(1) << endl;