pan class="o">=</span> <span class="n">length</span> <span class="o">-</span> <span class="nb">len</span><span class="p">(</span><span class="n">xf</span><span class="p">[:,</span> <span class="mi">0</span><span class="p">])</span>
        <span class="n">y</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">concatenate</span><span class="p">((</span><span class="n">xf</span><span class="p">,</span> <span class="n">np</span><span class="o">.</span><span class="n"