<span class="keyword">auto</span>&amp;&amp; [i, j, block] = A(index);</div>
<div class="line"><a id="l00045" name="l00045"></a><span class="lineno">   45</span>                   <span class="keyword">auto</span> seg_x           = x.segment&lt;N&gt;(j * N);</div>
<div class="line"><a id="l00046" name="l00046"></a><span class="lineno">   46</span> </div>
<div class="line"><a id="l00047" name="l00047"></a><span class="lineno">   47</span>                   Eigen::Vector&lt;T, N&gt; vec_x  = seg_x.as_eigen();<