top">Boost.Format</a> documentation
      for more details.
    </p>
<h4>
<a name="math_toolkit.error_handling.h4"></a>
      <span class="phrase"><a name="math_toolkit.error_handling.pole_error"></a></span><a class="link" href="error_handling.html#math_toolkit.error_handling.pole_error">Evaluation
      at a pole</a>
    </h4>
<p>
      When a special function is passed an argument that is at a pole without a well
      defined residual value, then the function returns the result of:
    </p>
<pre class="p