racy, Lanczos's smoothing differentiation is recommended
      as an alternative.
    </p>
<p>
      The default order of accuracy is 6, which reflects that fact that people tend
      to be interested in functions with many continuous derivatives. If your function
      does not have 7 continuous derivatives, is may be of interest to use a lower
      order method, which can be achieved via (say)
    </p>
<pre class="programlisting"><span class="keyword">double</span> <span class="identifier">d</span> <spa