title: Why can't I use fitted in class "ar"?
body: <p>I take fit model AR(2) for times series <code>chuoie</code>:</p>
  
  <pre><code>e      &lt;- c(101,82,66,35,31,7,20,92,154,125,85,68,38,23,10,24,83,132,131,118,
              90,67,60,47,41,21,16,6,4,7,14,34,45,43,48,42,28,10,8,2,0,1,5,12,14)
  chuoie &lt;- ts(e)
  fit    &lt;- ar.yw(chuoie, order=2)
  </code></pre>
  
  <p>And I want calculated values fitted for model fit AR(2):</p>
  
  <pre><code>fitted.values(fit)
  </code></pre>
  
  <p>Then I get:  </p>
  
  <pre><code>NULL
  </code></pre>
  
  <p>I don't understand the problem. If I use the <code>forecast</code> package, fit a model with <code>Arima(2,0,0)</code> and use <code>fitted</code>, then I will get results with no problems. Can you help me solve the problem?</p>