Figure 1

Node 1 with two incoming and one outgoing links is selected to be moved from its current position on the level j to a new position on the level j + 2. The associated energy difference is ΔE = -1 - 1 + 1 = -1 where two -1 contributions come from making (2, 1) and (3, 1) links hierarchical and the single +1 contribution comes from turning the link (1, 4) from hierarchical to anti-hierarchical.