span><span class="p">[</span><span class="n">species</span><span class="p">[</span><span class="n">j</span><span class="p">]]</span> <span class="o">+</span> <span class="n">tolerance</span>
            <span class="n">frac_diff</span> <span class="o">=</span> <span class="n">fc_diff</span><span class="p">[</span><span class="n">j</span><span class="p">]</span> <span class="o">-</span> <span class="n">fc_copy</span><span class="p">[</span><span class="n">i</span><span class="p">]</span>
            <span cl