an class="special">]</span> <span class="special">&lt;&lt;</span> <span class="char">'\t'</span> <span class="special">&lt;&lt;</span> <span class="identifier">x_vec</span><span class="special">[</span><span class="identifier">i</span><span class="special">][</span><span class="number">0</span><span class="special">]</span> <span class="special">&lt;&lt;</span> <span class="char">'\t'</span> <span class="special">&lt;&lt;</span> <span class="identifier">x_vec</span><span class="special">[</span><span class=