title: Using boost::accumulators, how can I reset a rolling window size, does it keep extra history?
body: <p>I am looking at the boost::accumulator framework, specifically a couple of the rolling_window calculations.</p>
  
  <pre><code>#include &lt;boost/accumulators/accumulators.hpp&gt;
  #include &lt;boost/accumulators/statistics/stats.hpp&gt;
  #include &lt;boost/accumulators/statistics/rolling_mean.hpp&gt;
  accumulator_set&lt;int, stats&lt;tag::rolling_mean&gt; &gt; acc(tag::rolling_window::window_size = 3);
  </code></pre>
  
  <p>As you see here, I have set the window_size to be three, such that it is maintaining the mean average of the last three samples only.</p>
  
  <p>Can I amend that size at run-time, perhaps based on a user setting?</p>
  
  <p>If so, and I increase the window_size does the accumulator have extra internal state if it had already seen more than my new window_size, or would I have to wait for the extra values?</p>