pecial">::</span><span class="identifier">vector</span><span class="special">&lt;</span><span class="keyword">double</span><span class="special">&gt;</span> <span class="identifier">d2vdt2</span> <span class="special">=</span> <span class="identifier">lanczos</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
</pre>
<p>
      For memory conscious programmers, you can reuse the memory space for the derivative
      as follows:
    </p>
<pre class="programlist