ix Halley iteration to handle zero derivative (with non-zero second derivative),
          see <a href="https://svn.boost.org/trac/boost/ticket/10046" target="_top">#10046</a>.
        </li>
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<h5>
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      <span class="phrase"><a name="math_toolkit.history1.math_1_9_1"></a></span><a class="link" href="history1.html#math_toolkit.history1.math_1_9_1">Math-1.9.1</a>
    </h5>
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