code: def add_dos(self, label, dos):
          
  
          densities = dos.get_smeared_densities(self.sigma) if self.sigma \
              else dos.densities
          self._doses[label] = {'frequencies': dos.frequencies, 'densities': densities}
docs: Adds a dos for plotting.
  
          Args:
              label:
                  label for the DOS. Must be unique.
              dos:
                  PhononDos object