span class="n">values</span><span class="p">[</span><span class="n">x</span><span class="p">]</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">occurrence</span><span class="o">.</span><span class="n">keys</span><span class="p">()])</span>
                <span class="n">pdf</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">gaussian_sum</span><span class="p">(</span><span class="n">centers</span><span class