title: All the zero values in upper triangle
body: <p>I've got the following code:</p>
  
  <pre><code>afs_in_sound &lt;- stringdistmatrix(soundexcode_termen, soundexcode_termen, method = 'hamming')
  </code></pre>
  
  <p>My matrix looks as follows:  </p>
  
  <pre><code>   0   1   inf   inf  
     1   0    0    inf  
     inf 0    0    inf   
     inf 0   inf    0 
  </code></pre>
  
  <p>I want to get all the indices for which the value is 0 in the upper triangle matrix. So here I want [2,3].</p>