\\[4pt] 0 &amp; \text{if } N = 1
\end{cases} \]</span> It is an error to call the <code>variance</code> function with an
array of size 0.</p>
<!-- real; sd; (real[] x); -->
<p></p>
<p><code>real</code> <strong><code>sd</code></strong><code>(real[] x)</code><br>
The sample standard deviation of elements in x. <span class="math display">\[ \text{sd}(x) =
\begin{cases} \sqrt{\, \text{variance}(x)} &amp; \text{if } N &gt; 1 \\[4pt]
0 &amp; \text{if } N = 0 \end{cases} \]</span> It is an error to call the <code>