docs: def _pathways_to_flux(self, paths, pathfluxes, n=None):
          r"""Sums up the flux from the pathways given
  
          Parameters
          -----------
          paths : list of int-arrays
          list of pathways
  
          pathfluxes : double-array
              array with path fluxes
  
          n : int
              number of states. If not set, will be automatically determined.
  
          Returns
          -------
          flux : (n,n) ndarray of float
              the flux containing the summed path fluxes
  
          """
          if (n is None):
              n = 0
              for p in paths:
                  n = max(n, np.max(p))
              n += 1
  
          # initialize flux
          F = np.zeros((n, n))
          for i in range(len(paths)):
              p = paths[i]
              for t in range(len(p) - 1):
                  F[p[t], p[t + 1]] += pathfluxes[i]
          return F