title: how to map a Eigen::Matrix to std::vector<Eigen::vector>?
body: <p>E.g., if I have an <code>Eigen::MatrixXd</code> of size 10 columns and 3 rows, how can I alias that to a <code>std::vector</code> of 10 elements of <code>Eigen::Vector3d</code>?
  when I say alias I mean using the same memory block without copying.</p>
  
  <p>I know that I can do the reversed mapping by something like:</p>
  
  <pre><code>std::vector&lt;Vector3d&gt; v(10);
  ...
  Map&lt;Matrix&lt;double,3,Dynamic&gt; &gt;  m(v.data().data(), 3, 10);
  </code></pre>
  
  <p>but reversely, if I have an Eigen::Matrix, I tried to convert it to a vector of Eigen::vector but the following code line failed compilation</p>
  
  <pre><code>Eigen::Matrix2Xd points;
  ...
  std::vector&lt;Eigen::Vector2d&gt; v_points(points.data()
      Eigen::aligned_allocator&lt;Eigen::vector2d&gt;(points_data()))
  </code></pre>