def flowDiff(graph1, graph2):
    """
    Return the difference between the flows of two graphs.

    Parameters
    ----------

    graph1: netwrorkx obj
    graph2: networkx obj

    Returns
    -------
    a dictionary with name od edge and diff in flows. graph1-graph2

    """
    flowDiff_ = {}
    for edge in graph1.edges():
        flow1 = graph1[edge[0]][edge[1]]['flow']
        flow2 = graph2[edge[0]][edge[1]]['flow']
        flowDiff_[edge] = flow1-flow2
    return flowDiff_