Exercise 9.15 Example IX.18: Although in the first 10 000 iterations the trace plots behaved well, when running the chains further it became apparent that the variance parameter σ got stuck at zero for one chain and that for quite some iterations. Apply the parameter expansion technique of Section 9.7 (adapt the program ‘chapter 9 arterio study.odc’) to improve convergence of this parameter. Does this change in the program alter your clinical conclusions?