The results in fig 6.1 are missing in the online version of the book. I can reproduce the chart in my own machine though. <img width="1318" alt="plot-book" src="https://user-images.githubusercontent.com/29334677/111984953-fb98d180-8b46-11eb-992f-0709e7164f78.png"> <img width="902" alt="plot-rstudio" src="https://user-images.githubusercontent.com/29334677/111985251-5a5e4b00-8b47-11eb-817c-ccb7576202f8.png">