title: Concatenation of 2 1D `numpy` Arrays Along 2nd Axis
body: <p>Executing</p>
  
  <pre><code>import numpy as np
  t1 = np.arange(1,10)
  t2 = np.arange(11,20)
  
  t3 = np.concatenate((t1,t2),axis=1)
  </code></pre>
  
  <p>results in a </p>
  
  <pre><code>Traceback (most recent call last):
  
    File "&lt;ipython-input-264-85078aa26398&gt;", line 1, in &lt;module&gt;
      t3 = np.concatenate((t1,t2),axis=1)
  
  IndexError: axis 1 out of bounds [0, 1)
  </code></pre>
  
  <p>why does it report that axis 1 is out of bounds?</p>