de>"log"</code> or <code>"identity"</code> as described in
<code><a href="flexsurvspline.html">flexsurvspline</a></code>.</p></dd>


<dt id="arg-spline">spline<a class="anchor" aria-label="anchor" href="#arg-spline"></a></dt>
<dd><p><code>"rp"</code> to use the natural cubic spline basis
described in Royston and Parmar.  <code>"splines2ns"</code> to use the
alternative natural cubic spline basis from the <code>splines2</code>
package (Wang and Yan 2021), which may be better behaved due to
the basis being or