title: Stacking Arrays in pylab using vstack
body: <p>I have to following code to stack arrays and solve a system of equations:</p>
  
  <pre><code> 1     import numpy as np
   2     from numpy.linalg import solve
  
   3     xi = np.array([-1., 1., -2])
   4     yi = np.array([0., 4., 3.])
   5     A = np.vstack([np.ones(3), xi, xi**2]).T
   6     b = yi
  
   7     c = solve(A,b)
  </code></pre>
  
  <p>Then After this I have code to execute a graph, But I get an error on the line 5. It says:</p>
  
  <pre><code>  TypeError: 'function' object has no attribute '__getitem__'
  </code></pre>
  
  <p>How can I fix this? </p>