SIMULATIONS

MODELS YOU CAN TOUCH

EDGEWORTH.SIM

Two agents exchange fixed totals of two goods. Set the initial allocation, run bilateral trades, and watch the allocation move toward the contract curve. Trades are proposed from the agents' marginal rates of substitution and accepted only when both agents end up strictly better off, so the allocation comes to rest at a point that is terminal under this bilateral trade rule — in these runs it lands near the contract curve.

A contours
B contours
Contract curve
Current trade path

A: u = x^0.25·y^0.75
B: u = x^0.75·y^0.25
Totals: X = Y = 1000.

A's X preference weight 0.25 B's X preference weight 0.75

A's X 800 A's Y 200

Live allocation and utility
Agent	X	Y	Utility
A	800	200	—
B	200	800	—

SPOT: — AVG: —

TRADES: 0 HISTORY: 0

Ready.

Reading the box

Agent A measures goods from the bottom-left corner; agent B measures from the top-right. Every point in the box is one way to split the fixed totals — 1000 units each of X and Y — between the two agents. Moving the point slides goods from one to the other.

Cobb-Douglas utility

Each agent values a bundle with u(x,y) = x^a·y^(1−a). Here a is the agent's X preference weight: it says how much of the agent's attention goes to good X, with the remainder going to Y. A larger weight makes X relatively more important to that agent. The sliders keep weights in the 0.05–0.95 range, so both goods always retain some value. These utility numbers are ordinal: they rank bundles for one agent and are not comparable between agents — a higher number for A does not mean A is "better off" than B.

Contours, MRS, and trades

The curved lines are indifference contours: bundles on one curve give that agent exactly the same utility. Changing a preference weight changes the shape and slope of that agent's contours. An agent's marginal rate of substitution (MRS) is the slope of its contour — how much Y it would give for one more unit of X. Proposed trades use a price midway between the two agents' MRS values, and a trade is applied only when both agents end up strictly better off.

The Pareto lens and the contract curve

The shaded lens around the current point marks allocations that would improve both agents at once. The amber contract curve is where the two agents' MRS values coincide; when no mutually improving trade remains, the allocation is terminal under this trade rule and in these runs it rests near that curve. That is a statement about this bilateral procedure, not a universal claim about welfare or markets.

Trails and prices

SPOT is the price (units of Y per unit of X) of the last accepted trade; AVG is the quantity-weighted average price over the whole run. The green dashed line is the current trade path, with its start circled; the muted lines and amber dots are earlier terminal endpoints. AUTO EXPLORE samples random starting allocations and proposes bids derived from the utilities at each point, so every trial under the current preference weights lands near the contract curve they define.

Build history: the OBSERVANDUM devlog →

ZI-TRADERS · GAME

A browser trading experiment with buyers, sellers and visible bids. Watch offers and trades unfold, then inspect the model through its devlog.

PLAY THE GAME ↗Devlog →

ZI-TRADERS · SIMULATOR

The React simulator exposes market settings in a parameter panel. Change the setup and compare the resulting trading activity with the animated build.

OPEN THE SIMULATOR ↗Screenshots & builds →

OTHER MODELS IN THE CABINET

COBB-DOUGLAS EXCHANGE

Two agents, adjustable Cobb-Douglas preferences and mutually beneficial trades approaching a contract curve. Devlog →

ZERO-INTELLIGENCE TRADERS

Trading experiments inspired by the zero-intelligence literature, with the rules and implementation recorded in the devlog. →

HOWITT–CLOWER MONEY EMERGENCE

Endogenous shops, private venues, a stylized public rail — finite-horizon evidence on what makes settlement infrastructure survive. Read more →

BLOCKCHAIN MINING TOY

A dungeon crawler where chests hold balances and minters issue blocks. Explore the game and its design history. →