ters given to <code>*_initial()</code> are assumed known.</p></dd>


<dt>taildown_type</dt>
<dd><p>The taildown covariance function type. Available options
include <code>"linear"</code>, <code>"spherical"</code>, <code>"exponential"</code>,
<code>"mariah"</code>, <code>"epa"</code>, and <code>"none"</code>.</p></dd>


<dt>euclid_type</dt>
<dd><p>The euclidean covariance function type. Available options
include <code>"spherical"</code>, <code>"exponential"</code>, <code>"gaussian"</code>,
<code>"cosine"</cod