title: Eigen::Matrix | Why does eigen expect an int and not size_t?
body: <p>According to the <a href="http://eigen.tuxfamily.org/dox-devel/classEigen_1_1Matrix.html" rel="nofollow">Eigen documentation</a>, the second and third template arguments, which correspond to number of rows and cols, are expected to be <code>int</code>. </p>
  
  <p>I am wondering why these arguments are not <code>size_t</code>? The only reason to have <code>int</code> there is, when eigen would allow to have negative number of rows or cols?</p>
  
  <p>The only reason why this could make sense is because of <code>Eigen::Dynamic</code>. Can anyone confirm that this is the reason to allow negative values for rows/cols?</p>