title: Multidimensional scaling (MDS) on iris dataset
body: <p>I should do multidimensional scaling with "mdscale" function in matlab on the famous Fisher Iris dataset.</p>
  
  <p>I don't get why sometimes it works and sometimes not. This is what I do:</p>
  
  <pre><code>clear all;
  load('fisheriris'); %it return a dataset in the variable "meas"
  
  distM = pdist(meas);  %creating the distance matrix of the dataset
  newPoints = mdscale(distM, 2, 'criterion', 'stress')    
  </code></pre>
  
  <p>The error is:</p>
  
  <blockquote>
    <p>Points in the configuration have co-located.  Try a different starting
    point, or use a different criterion.</p>
  </blockquote>
  
  <p>If I use another criterion like "sstress" or "metricsstress" it seems to work. </p>
  
  <p>How can it be explained? </p>