def METHOD_NAME(self, unknown=None, abstol=None, reltol=None):
    """
    Set the absolute and relative tolerance of one or more unknown
    quantities.
    :param unknown: A string or list of strings specifying the name(s) of the quantity/ies to set the tolerances for. If 'None', the tolerances are applied to all unknowns.
    :param float abstol: Absolut tolerance to set for unknown.
    :param float reltol: Relative tolerance to set for unknown.
    """
    if unknown is None:
        if reltol is None:
            raise Exception('If no unknown is specified, the default relative tolerance to use for the system must be specified.')
        self.reltol = float(reltol)
        self.overrides = []
    elif type(unknown) == str:
        t = self.getIndex(unknown)
        # Append to list or overwrite existing element?
        if t < 0:
            if abstol is None: abstol = 0
            if reltol is None: reltol = self.reltol
            self.overrides.append({'name': unknown, 'abstol': float(abstol), 'reltol': float(reltol)})
        else:
            if abstol is not None:
                self.overrides[t]['abstol'] = float(abstol)
            if reltol is not None:
                self.overrides[t]['reltol'] = float(reltol)
    elif type(unknown) == list:
        for u in unknown:
            self.METHOD_NAME(u, abstol=abstol, reltol=reltol)
    else:
        raise DREAMException("ToleranceSettings.set(): Unrecognized type of parameter 'unknown': {}.".format(type(unknown)))