mpendiet/diffint.pdf" target="_top">here</a>.
    </p>
<p>
      Despite the effort that has went into choosing a reasonable value of <span class="emphasis"><em>h</em></span>,
      the problem is still fundamentally ill-conditioned, and hence an error estimate
      is essential. It can be queried as follows
    </p>
<pre class="programlisting"><span class="keyword">double</span> <span class="identifier">error_estimate</span><span class="special">;</span>
<span class="keyword">double</span> <span class="id