ions corresponding to multiple chains. When there are fewer of
those leading dimensions than there are chain dimensions, the corresponding
dimensions in the <code>log_accept_prob</code> are averaged (in the direct space, rather
than the log space) before being used to adjust the step size. This means that
this kernel can do both cross-chain adaptation, or per-chain step size
adaptation, depending on the shape of the step size.</p>
<p>For example, if your problem has a state with shape <code>[S]</code>, your