"><span class="pre">cumprod</span></tt>, <tt class="docutils literal"><span class="pre">geo_mean</span></tt>, <tt class="docutils literal"><span class="pre">sqrt</span></tt>.</li>
</ul>
<p>A valid posynomial expression is</p>
<ul class="simple">
<li>a valid monomial;</li>
<li>the sum of two or more posynomials;</li>
<li>the product of two or more posynomials;</li>
<li>the ratio of a posynomial and a monomial;</li>
<li>a posynomial raised to a positive integral power; or</li>
<li>a call to one of the followi