def visibility_graph(series):

     g = nx.Graph()

     # convert list of magnitudes into list of tuples that hold the index

     tseries = []

     n = 0

     for magnitude in series:

         tseries.append((n, magnitude))

         n += 1

     '''add nodes'''

     for i in range(len(tseries)):

         (ta, ya) = tseries[i]

         g.add_node(ta, mag=ya)

     '''add edges'''

     for a, b in combinations(tseries, 2):

         (ta, ya) = a

         (tb, yb) = b

         connect = True

         if tb - ta > 1:

             (tc, yc) = max(tseries[ta + 1:tb])  #我的算法

             print(tc,yc)

             if (yc > yb + (ya - yb) * ((tb - tc) / (tb - ta))):

                 connect = False

         # medium = tseries[ta+1 :tb]  #别人的算法

         # for tc, yc in medium:

         #     if yc > yb + (ya - yb) * ((tb - tc) / (tb - ta)):

         #         connect = False

         if connect:

             g.add_edge(ta, tb)

     return g