title: Sum corresponding elements between two multidimensional arrays
body: <p>Suppose that I have two arrays, and I want to add the corresponding elements.</p>
  <pre><code>$v_4 = [
      [1, 2, 3], 
      [4, 5, 6],
  ];
  $v_5 = [
      [7, 8, 9], 
      [10, 11, 12], 
  ];
  </code></pre>
  <p>How should I construct an addition function to add across these arrays to get:</p>
  <pre><code>[
      [8, 10, 12], 
      [14, 16, 18],
  ]
  </code></pre>
  <p>I know I need to utilise <a href="http://php.net/manual/de/function.array-map.php" rel="nofollow noreferrer"><code>array_map</code></a> somehow, but I am unsure how to proceed in this multidimensional case.</p>