 used to evaluate the ODE system</p></li>
<li><p><em><code>x_r</code></em>, data values used to evaluate the ODE system</p></li>
<li><p><em><code>x_i</code></em>, integer data values used to evaluate the ODE system.</p></li>
</ul>
<p>The ODE system function separates parameter values, <em><code>theta</code></em>, from
data values, <em><code>x_r</code></em>, for efficiency in computing the gradients of the
ODE.</p>
</div>
<div id="non-stiff-solver" class="section level3">
<h3 number="9.2.2"><span class="head