de-with-copy"><code class="sourceCode stan"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="kw">target +=</span> normal_lpdf(y | mu, sigma);</span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a>mu = a + b * x;</span></code><button title="Copy to Clipboard" class="code-copy-button"><i class="bi"></i></button></pre></div>
<p>To trap these kinds of errors, variables are initialized to the special not-a-number (<code>NaN</code>) value. If <code>NaN</c