><img src="../../../../equations/ellint2.png"></span>
        </p>
<p>
          Requires -1 &lt;= k &lt;= 1, otherwise returns the result of <a class="link" href="../../main_overview/error_handling.html#domain_error">domain_error</a>.
        </p>
<p>
          The final <a class="link" href="../../policy.html" title="Policies">Policy</a> argument is
          optional and can be used to control the behaviour of the function: how
          it handles errors, what level of precision to use etc. Refer to the