pan class="special">;</span>  <span class="comment">// one of the two radii of the ellipse</span>
<span class="special">};</span> <span class="comment">// template &lt;class T&gt; struct elliptic_root_functor_noderiv</span>
</pre>
<p>
        We'll also need a decent estimate to start searching from, the approximation:
      </p>
<pre class="programlisting">L(a, b) &#8776; 4&#8730;(a<sup>2</sup> + b<sup>2</sup>)</pre>
<p>
        Is easily inverted to give us what we need, which using derivative-free root
 