Gives the conductivity (1/Ohm*m) in either a full 3x3 tensor
            form, as 3 eigenvalues, or as the average value
            (trace/3.0) If doping_levels=True, the results are given at
            different p and n doping
            levels (given by self.doping), otherwise it is given as a series
            of electron chemical potential values

            Args:
                output (string): the type of output. 'tensor' give the full
                3x3 tensor, 'eigs' its 3 eigenvalues and
                'average' the average of the three eigenvalues
                doping_levels (boolean): True for the results to be given at
                different doping levels, False for results
                at different electron chemical potentials
                relaxation_time (float): constant relaxation time in secs

            Returns:
                If doping_levels=True, a dictionary {temp:{'p':[],'n':[]}}.
                The 'p' links to conductivity
                at p-type doping and 'n' to the conductivity at n-type
                doping. Otherwise,
                returns a {temp:[]} dictionary. The result contains either
                the sorted three eigenvalues of the symmetric
                conductivity tensor (format='eigs') or a full tensor (3x3
                array) (output='tensor') or as an average
                (output='average').
                The result includes a given constant relaxation time

                units are 1/Ohm*m

def get_conductivity(self, output='eigs', doping_levels=True,
                         relaxation_time=1e-14):
        """
            Gives the conductivity (1/Ohm*m) in either a full 3x3 tensor
            form, as 3 eigenvalues, or as the average value
            (trace/3.0) If doping_levels=True, the results are given at
            different p and n doping
            levels (given by self.doping), otherwise it is given as a series
            of electron chemical potential values

            Args:
                output (string): the type of output. 'tensor' give the full
                3x3 tensor, 'eigs' its 3 eigenvalues and
                'average' the average of the three eigenvalues
                doping_levels (boolean): True for the results to be given at
                different doping levels, False for results
                at different electron chemical potentials
                relaxation_time (float): constant relaxation time in secs

            Returns:
                If doping_levels=True, a dictionary {temp:{'p':[],'n':[]}}.
                The 'p' links to conductivity
                at p-type doping and 'n' to the conductivity at n-type
                doping. Otherwise,
                returns a {temp:[]} dictionary. The result contains either
                the sorted three eigenvalues of the symmetric
                conductivity tensor (format='eigs') or a full tensor (3x3
                array) (output='tensor') or as an average
                (output='average').
                The result includes a given constant relaxation time

                units are 1/Ohm*m
        """
        return BoltztrapAnalyzer._format_to_output(self._cond,
                                                   self._cond_doping, output,
                                                   doping_levels,
                                                   relaxation_time)