title: 'tuple' object is not callable error using matplotlib library?
body: <pre><code>1  def auto_correlate(x):
  2     cor = np.correlate(x,x,mode="full")
  3     return cor[N-1:]
  
  4  c = np.zeros(N)
  5  c = auto_correlate(x-ave)/N
  6  plt.plot(c)
  7  plt.xlim(-1000, 10000)
  8  plt.xlabel(r'$i$',fontsize=16)
  9  plt.ylabel(r'$\varphi(i)$',fontsize=16)
  10 print('\sigma^2 = ', std**2)
  11 plt.show()
  </code></pre>
  
  <p>Why do I keep getting error 'tuple' object not callable online 7 ? please explain</p>