title: How to get the number of columns in a matrix?
body: <p>Suppose I specify a matrix <code>A</code> like</p>
  
  <pre><code>A = [1 2 3; 4 5 6; 7 8 9]
  </code></pre>
  
  <p>how can I query <code>A</code> <strong>(without using <code>length(A)</code>)</strong> to find out it has 3 columns?</p>