class_docstr: A simple graph class
  
      
code: def add_edge(self, n, m, ws=True, wp=True):
      self.succ[n][m] = ws
      self.pred[m][n] = wp
  
file_path: dipy/dipy/core/graph.py
label_desc: Use image node_id 3 for calling the Graph obj's underlying member method code with example usage: obj.add_edge(n, m, ws, wp) without return types