title: Community detection and comparison in igraph
body: <p>I am using the <code>multilevel</code> algorithm in <code>igraph</code> to detect communities among the same set of the nodes <em>over a period of time</em> (i.e. multiple and potentially different clusterings will be produced for the same set of nodes). I have two questions regarding the output of the detection algorithm (which may also apply to other detection algorithms in <code>igraph</code>):</p>
  
  <ol>
  <li><p>How does the algorithm decide the membership assignment? In other words, is there any rule or pattern that decides which nodes are assigned to the 1st subgraph of the resulted <code>VertexClustering</code> object and which ones will be assigned to the 2nd subgraph, and so on?</p></li>
  <li><p>If there is some consistent membership assignment pattern, is there a method to compare the membership of two communities that are detected at different times?</p></li>
  </ol>