title: R, incomplete elements in time series decomposition
body: <p>I am using below codes to perform time series decomposition.</p>
  
  <pre><code>a &lt;- c( 4, 3, 2, 12, 6, 6, 13, 9, 9, 11, 8, 6, 15, 3, 3, 4, 4, 12, 14, 11, 3, 10, 5, 5)
  
  ts_a = ts(a, frequency = 12)
  
  decompose_a = decompose(ts_a, 'additive')
  plot(decompose_a)
  
  decompose_a = decompose(ts_a, 'multiplicative')
  plot(decompose_a)
  </code></pre>
  
  <p>The plot shows the trend decomposed is incomplete. How should I interpret this?</p>
  
  <p>Is it no complete trend can be extracted from this time series? (likewise the randomness)</p>
  
  <p>Thank you.</p>
  
  <p><a href="https://i.stack.imgur.com/RzVQI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RzVQI.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/GHpJt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GHpJt.png" alt="enter image description here"></a></p>