nstants" class="section level2">
<h2><span class="header-section-number">3.2</span> Mathematical Constants</h2>
<p>Constants are represented as functions with no arguments and must be
called as such. For instance, the mathematical constant <span class="math inline">\(\pi\)</span> must be
written in a Stan program as <code>pi()</code>.</p>
<!-- real; pi; () -->
<p></p>
<p><code>real</code> <strong><code>pi</code></strong><code>()</code><br>
<span class="math inline">\(\pi\)</span>, the ratio of a circleâ€