title: Cross product of a vector in NumPy
body: <p>Consider the following vectors (essentially<code>2x1</code> matrices):</p>
  
  <pre><code>a = sc.array([[1], [2], [3]])
  &gt;&gt;&gt; a
  [[1]
   [2]
   [3]]
  
  b = sc.array([[4], [5], [6]])
  &gt;&gt;&gt; b
  [[4]
   [5]
   [6]]
  </code></pre>
  
  <p>The cross product of these vectors can be calculated using <code>numpy.cross()</code>. Why does this not work:</p>
  
  <pre><code>import numpy as np 
  
  np.cross(a, b)
  ValueError: incompatible dimensions for cross product
  (dimension must be 2 or 3)
  </code></pre>
  
  <p>but this does?:</p>
  
  <pre><code>np.cross(a.T, b.T)
  [[-3  6 -3]]
  </code></pre>