Fig. 2
The number of patents, combinations of technology codes and technology codes as inventions accumulate in the system. (a) Shows the increase in these quantities over time. (b) Shows their increase as functions of the number of patents. The red solid line is a linear fit with combinations C. The grey dashes in (b) mark the number of patents for the years shown. Because the number of patents increases approximately exponentially in time, the gaps between year marks get shorter and shorter as one moves to the right of panel (b). Reprinted from (Youn et al. 2015) under the Creative Commons license