pan> <span class="identifier">Q</span> <span class="special">=</span> <span class="identifier">integrator</span><span class="special">.</span><span class="identifier">integrate</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">constants</span><span class="special">::</span><span class="identifier">half_pi</span><span class="special">&lt;</span><span class="keyword">double</s