title: invalid initialization of non-const reference of type from an rvalue of type for arma::subvec
body: <p>The vector <code>y_long_name</code> has 100 members and I plan to manipulate only a subvector of it made of first three members. The <code>subvector</code> function is used in my code like a left value:</p>
  
  <pre><code>y_long_name.subvec(0,2)=A*x1;
  </code></pre>
  
  <p>However C++ does not recognize it as a left value. How can I define <code>yr</code> to be used instead of <code>y_long_name.subvec(0,2)</code>?</p>
  
  <p>what I want to do is to use the short form <code>yr</code> instead of <code>y_long_name.subvec(0,2)</code> but without using macro.</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;armadillo&gt;
  
  int main()
  {
      const arma::vec::fixed&lt;3&gt; x1={1.2,3.5,-0.27};   
      arma::mat::fixed&lt;3,3&gt; A={{5,3,6},{8,2,11},{7,5,9}};
  
      arma::vec::fixed&lt;3&gt; y1=A*x1; // ok
  
      arma::vec::fixed&lt;100&gt; y_long_name;
      y_long_name.subvec(0,2)=A*x1; // ok
  
      arma::vec::fixed&lt;3&gt;&amp; yr=y_long_name.subvec(0,2);
      yr=A*x1;
  
      y_long_name.print();
  
      return 0;
  }
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>test.cpp: In function ‘int main()’:
  test.cpp:14:48: error: invalid initialization of non-const reference of type ‘arma::Col&lt;double&gt;::fixed&lt;3ull&gt;&amp;’ from an rvalue of type ‘arma::subview_col&lt;double&gt;’
    arma::vec::fixed&lt;3&gt;&amp; yr=y_long_name.subvec(0,2)
  </code></pre>