ctor, or a character vector of parameter names, which must be a subset
  of those supplied in <code>par_names</code> in the call to
  <code><a href="adjust_loglik.html">adjust_loglik</a></code> that produced <code>object</code>.</p>
<p><code>which_pars</code> must not have any parameters in common with
  <code>attr(object, "fixed_pars")</code>.  <code>which_pars</code> must not contain
  all of the unfixed parameters, i.e. there is no point in profiling over
  all the unfixed parameters.</p>
<p>If missing, 