title: Difference between adjacent elements - diagonal direction
body: <p>I have a matrix, I =</p>
  
  <pre><code> 5     4     3
   9     8     6
   6     3     4
  </code></pre>
  
  <p>How can I calculate differences between adjacent elements in a diagonal directions. I want these outputs(for first and last rows and columns I don't mind padding):</p>
  
  <pre><code>  5     4     3
    5     5     6
    2    -3     4
  </code></pre>
  
  <p>and</p>
  
  <pre><code> 5     4     3
   9     3     2
   6    -6    -4
  </code></pre>