> <span class="identifier">sin_theta</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">sqrt</span><span class="special">(</span><span class="number">1</span> <span class="special">-</span> <span class="identifier">cos_theta</span> <span class="special">*</span> <span class="identifier">cos_theta</span><span class="special">);</span>
<span class="keyword">double</span> <span class="identifier">phi</span> <span class="special">=</s