Seven models about what happens when agents aren’t just following rules — they’re choosing strategies, building networks, and designing institutions. From game theory to governance, these essays explore how interdependence shapes outcomes.
The Girvan-Newman algorithm (2002) discovers hidden groups by iteratively removing the edges that carry the most shortest-path traffic. It reveals the principle that boundaries between communities are where the information flows.
Leontief's input-output model (1936) tracks the web of purchases between sectors of an economy. A change in demand for one sector ripples through all the others — and the total effect is always larger than the direct effect.
Axelrod's tournament (The Evolution of Cooperation, 1984) pitted strategies against each other in a repeated prisoner's dilemma. The winner was the simplest entry: Tit for Tat — cooperate first, then mirror. No cleverness required.
Kriging (Krige, 1951; Matheron, 1963) uses spatial correlation to produce optimal predictions from scattered samples. Unlike simpler methods, it quantifies its own uncertainty — you get both a map and a measure of how much to trust it.
Nash equilibrium (Nash, 1950) is the point where every player is doing the best they can, given what everyone else is doing. Often self-interest and the common good align — and when they don't, understanding the equilibrium reveals exactly how to redesign the rules so that they do.
Sen's critique ("Rational Fools," 1977) dismantles the orthodox assumption that choice, preference, and welfare are one and the same. A single ordering cannot capture commitment, adaptive desires, or the liberal paradox — and treating it as if it can produces policies that mistake deprivation for satisfaction.
Ostrom's governance framework (Governing the Commons, 1990) dismantles the assumption that shared resources inevitably collapse. Communities worldwide have sustained fisheries, forests, and pastures for centuries — not through privatization or state control, but through institutional design: communication, monitoring, and graduated sanctions.