a transform of the scale or
deviation parameter <code>sigma_y</code>. It is defined in the generated
quantities block because it is not used in the model. Making it
a generated quantity allows it to be monitored for convergence (being
a non-linear transform, it will have different autocorrelation and
hence convergence properties than the deviation itself).</p>
<p>In later versions of Stan which have random number generators for
the distributions, the <code>generated quantities</code> block will be
usable to