In first place, great article for the "Computational Complexity".
I've some question about what's written in the article.
1 - In the example 6 of section of the "More recursion trees", you say that in the second level of the tree, we've a complexity of c(N/2)^3. Why not c(N/3)^3?
2 - Why the time to process each of them decreases to one eighth of the original time?
3 - You say that the geometric progression has the sum of:
Why do you put (1-3/8)? What do you want to say?
4 - You say that in the example 6, "as we go deeper in the tree, the total amount of work on the current level decreases.", but in the example 7 "as we go deeper in the tree, the total amount of work on the current level increases.". Why the amount of work in 7 increases and in 6 decreases, if, on going to a deeper level in both examples, the problem is divided in more subproblems?