"sd">                specified properties in a sparse array.</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="n">occurrence</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">get_element_occurrence</span><span class="p">(</span><span class="n">system</span><span class="p">)</span>
        <span class="n">weights</span> <span class="o">=</span> <span class="n">np</span><span class="o">.</span><span class="n">array</span><span clas