def _vasp5_lines_is_selective_dynamics(poscar_lines):
    """Returns true if selective dynamics has been turned on for
    the poscar files

    Parameters
    ----------
    poscar_lines : list of str

    Returns
    -------
    bool

    """
    tag=poscar_lines[7].split()[0][0]
    if tag in "sS":
        return True
    else:
        return False