ve, so our functor will be at least twice as expensive
        to call as the derivative-free one above: we'll have to reduce the iteration
        count quite substantially to make a difference!
      </p>
<p>
        Here's the revised functor:
      </p>
<pre class="programlisting"><span class="keyword">template</span> <span class="special">&lt;</span><span class="keyword">class</span> <span class="identifier">T</span> <span class="special">=</span> <span class="keyword">double</span><span class="special