ords_der</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">np</span><span class="o">.</span><span class="n">vstack</span><span class="p">((</span><span class="n">sample_index</span><span class="p">,</span> <span class="n">i_der</span><span class="o">.</span><span class="n">coords</span><span class="p">)))</span>
                    <span class="k">else</span><span class="p">:</span>
                        <span class="n">derivatives</span><span class="p">[</