def METHOD_NAME(traj):
    """Compute the principal moments of a trajectory.
    For each frame calculate the eigenvalues of the gyration tensor.
    Parameters
    ----------
    traj : Trajectory
        Trajectory to compute gyration tensor of.
    Returns
    -------
    evecs:  np.ndarray, shape=(traj.n_frames, 3), dtype=float64
        Principal moments for each frame in ascending order.
    """
    gyration_tensor = compute_gyration_tensor(traj)
    return np.linalg.eigvalsh(gyration_tensor)