网格线不显示

我设置了以下代码来读取 .graphml 文件，执行计算（特征值），然后绘制结果。这是我到目前为止的代码：

import numpy as np
import networkx as nx
import matplotlib.pyplot as plt

# Read in the Data

G = nx.read_graphml("/home/user/DropBox_External_Datasets/JHU_Human_Brain/cat_brain_1.graphml")

nx.draw(G)
plt.savefig("test_graph.png")

Z = nx.to_numpy_matrix(G)

# Get Eigenvalues and Eigenvectors
# ----------------------------------------------------------------------------------
#
e_vals, e_vec = np.linalg.eigh(Z)

print("The eigenvalues of A are:", e_vals)
print("The size of the eigenvalues matrix is:", e_vals.shape)
# ----------------------------------------------------------------------------------

plt.plot(e_vals, 'g^')
plt.ylabel('Eigenvalues')
# plt.axis([-30, 300, -15, 30]) # Optimal settings for Rhesus data
# plt.axis([-0.07, 1, -0.2, 1.2])  # range to zoom in on cluster of points in Rhesus data

plt.grid(b=True, which='major', color='b', linestyle='-')
plt.show()

但图表上没有显示网格线或轴。那还有别的事吗plt.grid()我需要使用什么？

我一直发现使用matplotlib面向对象的API https://matplotlib.org/stable/api/index.html#the-object-oriented-api是一种让事情按预期进行的更稳健的方式。Pyplot 本质上是面向对象调用的一个大包装。我写了一些应该等效的东西：

import matplotlib.pyplot as plt

# ... your other code here

# Using subplots
fig, ax = plt.subplots(ncols=1, nrows=1) # These arguments can be omitted for one
                                         # plot, I just include them for clarity
ax.plot(e_vals, 'g^')
ax.set_ylabel('Eigenvalues')

ax.grid(b=True, which='major', color='b', linestyle='-')

plt.show()