title: numpy.r_ place the the 1’s in the mid
body: <p>I am reading <a href="https://numpy.org/doc/stable/reference/generated/numpy.r_.html#numpy.r_" rel="nofollow noreferrer">numpy.r_  docs</a>.  I get it that I cannot place the 1’s at the mid position.
  For example ,</p>
  <p><code>a = np.array( [[3,4,5],[ 33,44,55]])</code></p>
  <p><code>b = np.array( [[-3,-4,-5],[ -33,-44,-55]])</code></p>
  <p><code>np.r_['0,3,1',a,b]</code></p>
  <p>Actually firstly the shape (2,3) of <code>a</code> is upgraded to shape (1,2,3) and the same  as <code>b</code>.Then plus the two shape (1,2,3) + (1,2,3) = (2,2,3) is the final shape of result, note I only plus the first number since the '0' in the '0,3,1'.</p>
  <p>Now the question is that according the docs, I can upgrade the shape of  <code>a</code> to shape(1,2,3) or (2,3,1) ,but how can upgrade to the shape (2,1,3) ?</p>