def METHOD_NAME(
        self,
        ):
    """Write down the RMSD matrix."""
    output_fname = Path(self.path, self.output_name)
    # check if there are very low values in the RMSD vector
    check_low_values = np.isclose(
        self.data[:, 2],
        np.zeros(self.npairs),
        atol=0.1
        ).any()
    if check_low_values:
        log.warning(f"core {self.core}: low values of RMSD detected.")
    with open(output_fname, "w") as out_fh:
        for data in list(self.data):
            data_str = f"{data[0]:.0f} {data[1]:.0f} {data[2]:.3f}"
            data_str += os.linesep
            out_fh.write(data_str)