ariables in their argument expressions.</p>
<div id="specifying-an-ordinary-differential-equation-as-a-function" class="section level3">
<h3 number="9.2.1"><span class="header-section-number">9.2.1</span> Specifying an Ordinary Differential Equation as a Function</h3>
<p>A system of ODEs is specified as an ordinary function in Stan within
the functions block. The ODE system function must have this function
signature:</p>
<pre><code> real[] ode(real time, real[] state, real[] theta,
            real[] x_r, i