Polyhedron/external/eigen-3.4.0/doc/snippets/ComplexEigenSolver_eigenvalues.cpp

MatrixXcf ones = MatrixXcf::Ones(3,3);
ComplexEigenSolver<MatrixXcf> ces(ones, /* computeEigenvectors = */ false);
cout << "The eigenvalues of the 3x3 matrix of ones are:" 
     << endl << ces.eigenvalues() << endl;