title: Eigen3: coefficient-wise multiplication in place
body: <p>How can you perform a element-wise multiplication in place using Eigen3?</p>
  
  <p>Does</p>
  
  <pre><code>a = a.cwiseProduct(b);
  </code></pre>
  
  <p>run in place? Or is</p>
  
  <pre><code>a.array() *= b.array();
  </code></pre>
  
  <p>the better solution in terms of style and performance?</p>