n><span class="n">istart</span><span class="w"> </span><span class="p">,</span><span class="w"> </span><span class="n">iend</span>
<span class="w">               </span><span class="nb">sum</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">sum</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">Z</span><span class="p">(</span><span class="n">j</span><span class="p">)</span>
<span class="w">            </span><span class="