nk" href="error_handling.html#math_toolkit.error_handling.underflow_error">Numeric
      Underflow</a>
    </h4>
<p>
      If the result of a special function is known to be non-zero, but the calculated
      result underflows to zero, then the function returns the result of:
    </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">math</span><span class="special">::</span><span class="identifier">policies</span><span class="special">: