title: Why does classification accuracy of K-means clustering decrease with more training data?
body: <p>I want to classify actions from videos. For this purpose, K-means clustering is applied to optical flow points to generate a codebook.</p>
  
  <p>With <code>k=200</code>, accuracy is initially 85%. After adding training data, accuracy is 50%. If <code>k=400</code>, accuracy is back to 85%.</p>
  
  <p>How can the value of <code>k</code> be automatically optimized for my training data?</p>