code>1e-200</code> may be represented, but
<code>1e-200 * 1e-200</code> underflows so that the result is zero.</p>
<p>Underflow is a ubiquitous problem in likelihood calculations,
For example, if <span class="math inline">\(p(y_n \mid \theta) &lt; 0.1\)</span>, then</p>
<p><span class="math display">\[
p(y \mid \theta) = \prod_{n=1}^N p(y_n \mid \theta)
\]</span></p>
<p>will underflow as soon as <span class="math inline">\(N &gt; 350\)</span> or so.</p>
<p>To deal with underflow, work on the log scale. Even