title: Linspace in numpy library
body: <p>I want to draw 3d lines using Python. I used Matplotlib, but I have a problem with the <code>linspace</code> function, and <code>Axes3D</code>. 
  I already included MatplotLib and numpy library to the project.</p>
  
  <p>this is the code : </p>
  
  <pre><code>import matplotlib as mpl
  from mpl_toolkits.mplot3d import Axes3D
  import numpy as np
  import matplotlib.pyplot as plt
  
  mpl.rcParams['legend.fontsize'] = 10
  
  fig = plt.figure()
  ax = fig.gca(projection='3d')
  theta = np.linspace(-4 * np.pi, 4 * np.pi, 100)
  z = np.linspace(-2, 2, 100)
  r = z**2 + 1
  x = r * np.sin(theta)
  y = r * np.cos(theta)
  ax.plot(x, y, z, label='parametric curve')
  ax.legend()
  
  plt.show()
  </code></pre>
  
  <p>this picture will clarify the code bugs and the libraries: 
  <a href="http://store1.up-00.com/2015-04/1429377578131.png" rel="nofollow">picture</a></p>