lass="nb">len</span><span class="p">(</span><span class="n">centers</span><span class="p">)</span>

        <span class="c1"># Initialize numpy arrays for storing the descriptor and derivatives.</span>
        <span class="k">if</span> <span class="n">return_descriptor</span><span class="p">:</span>
            <span class="n">c</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">init_descriptor_array</span><span class="p">(</span><span class="n">n_centers</sp