Question

我尝试了以下代码，以找到负循环。运行代码时遇到错误：“ NameError：未定义名称'NetworkXUnbounded'”

我正在尝试在此处运行bellman-ford算法。 Algo引发了一个类型为“ NetworkXUnbounded”的异常，我尝试使用下面显示的异常处理来处理。

import pandas as pd 
import networkx as nx
import numpy as np
df = pd.read_csv("fx_rate_3.csv") 
G = nx.from_pandas_edgelist(df,source='A', target='B', edge_attr ['weight'], create_using=nx.DiGraph())

def find_path(digraph, start):
    try:
        path = nx.bellman_ford_predecessor_and_distance(digraph, start, 'weight') 
        return path
    except NetworkXUnbounded:
        cycles = nx.simple_cycles(digraph)
        for cycle in cycles:
            print (cycle)

Answer 1

在使用之前，您需要先从NetworkXUnbounded模块导入networkX。像这样：

import pandas as pd 
import networkx as nx
import numpy as np
from networkx import NetworkXUnbounded  # <---- Import the exception before using it

df = pd.read_csv("fx_rate_3.csv") 
G = nx.from_pandas_edgelist(df,source='A', target='B', edge_attr ['weight'], create_using=nx.DiGraph())

def find_path(digraph, start):
    try:
        path = nx.bellman_ford_predecessor_and_distance(digraph, start, 'weight') 
        return path
    except NetworkXUnbounded:
        cycles = nx.simple_cycles(digraph)
        for cycle in cycles:
            print (cycle)

还要注意，即使无向图中存在负权重边缘，也会发生此异常：

如果（di）图包含负成本（di）周期，则该算法会引发异常，以指示存在负成本（di）周期。注意：无向图中的任何负权重边缘都是负成本周期。

有关更多信息，请参见the documentation。

在图中找到负周期

1 个答案: