code: def lmax(self):
          r
          if self._lmax is None:
              self.logger.warning('The largest eigenvalue G.lmax is not '
                                  'available, we need to estimate it. '
                                  'Explicitly call G.estimate_lmax() or '
                                  'G.compute_fourier_basis() '
                                  'once beforehand to suppress the warning.')
              self.estimate_lmax()
          return self._lmax
docs: r"""Largest eigenvalue of the graph Laplacian.
  
          Can be exactly computed by :func:`compute_fourier_basis` or
          approximated by :func:`estimate_lmax`.