an><span class="mf">1.6</span><span class="p">,</span> <span class="n">b3</span><span class="o">=</span><span class="mf">2.0</span><span class="p">,</span> <span class="n">b4</span><span class="o">=</span><span class="mi">30</span><span class="p">),</span>
    <span class="p">)</span>

<span class="c1"># source frame</span>
<span class="n">rate1_src</span> <span class="o">=</span> <span class="n">cbc</span><span class="o">.</span><span class="n">merger_rate_density</span><span class="p">(</span><span class=