title: How to merge elements in a matrix
body: <pre><code>x = [1 2 3 4 5
       1 2 3 0 0];
  </code></pre>
  
  <p>I want to get off all zeros and merge the two rows</p>
  
  <pre><code>newx = x(:,1) + x(:,2)(nonzeros)
       = [1 2 3 4 5 1 2 3];
  </code></pre>