title: Gridlines not showing up
body: <p>I've set up the following code to read in a .graphml file, preform a calculation (eigenvalues) and then plot the results. Here is the code I have so far:     </p>
  
  <pre><code>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()
  </code></pre>
  
  <p>But no gridlines or axes show up on the graph. Is there something other then <code>plt.grid()</code> that I need to use? </p>