ror</span></code> C++ exception.
    </p>
<h4>
<a name="math_toolkit.error_handling.h8"></a>
      <span class="phrase"><a name="math_toolkit.error_handling.evaluation_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.evaluation_error">Evaluation
      Errors</a>
    </h4>
<p>
      When a special function calculates a result that is known to be erroneous,
      or where the result is incalculable then it calls:
    </p>
<pre class="programlisting"><span class="identifi