span class="o">=</span> <span class="n">num_rows</span> <span class="o">//</span> <span class="mi">2</span>
        <span class="n">left</span><span class="p">[</span><span class="mi">0</span><span class="p">:</span><span class="n">half_nrows</span><span class="p">,</span> <span class="mi">0</span><span class="p">:</span><span class="n">half_nrows</span><span class="p">]</span> <span class="o">=</span> <span class="n">left_mats</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
