old_contents: """Reference implementations of graph algorithms."""
  import numpy as np
  
  
  def bellman_ford_reference(A, c):
      """Execute reference implementation of Bellman-Ford.
  
      Parameters
      ----------
      A : coo sparse matrix
          n x n directed graph with positive weights
  
      c : array_like
          list of cluster centers
  
      Return
      ------
      m : ndarray
          cluster index
  
      d : ndarray
          distance to cluster center
  
      See Also
      --------
      amg_core.graph.bellman_ford
  
      """
      Nnode = A.shape[0]
      d = np.full((Nnode,), np.inf)
      m = np.full((Nnode,), -1.0, dtype=np.int32)
  
      d[c] = 0  # distance
      m[c] = c  # index
  
      done = False
      while not done:
          done = True
          for i, j, Aij in zip(A.row, A.col, A.data):
              if Aij > 0 and d[i] + Aij < d[j]:
                  d[j] = d[i] + Aij
                  m[j] = m[i]
                  done = False
  
      return (d, m)
  
new_contents: """Reference implementations of graph algorithms."""
  import numpy as np
  
  
  def bellman_ford_reference(A, c):
      """Execute reference implementation of Bellman-Ford.
  
      Parameters
      ----------
      A : coo sparse matrix
          n x n directed graph with positive weights
  
      c : array_like
          list of cluster centers
  
      Returns
      -------
      m : ndarray
          cluster index
  
      d : ndarray
          distance to cluster center
  
      See Also
      --------
      amg_core.graph.bellman_ford
  
      """
      Nnode = A.shape[0]
      d = np.full((Nnode,), np.inf)
      m = np.full((Nnode,), -1.0, dtype=np.int32)
  
      d[c] = 0  # distance
      m[c] = c  # index
  
      done = False
      while not done:
          done = True
          for i, j, Aij in zip(A.row, A.col, A.data):
              if Aij > 0 and d[i] + Aij < d[j]:
                  d[j] = d[i] + Aij
                  m[j] = m[i]
                  done = False
  
      return (d, m)
  
subject: fix return docstring