cwheat@mit: networks & organization

This simulation is a replication of Hummon's agent-based model of tie formation in a network. Each actor is colored to indicate her utility—the numerical value of her utility is indicated in the node label as well. Actors with relatively high utility are indicated by warmer colors, and actors with low utility are indicated by cooler colors.

The four buttons in the upper left allow you to control the progress of the simulation. Each step of the simulation corresponds to a choice by a randomly selected actor to change her tie with other actors. To choose or setup a network to simulate exchange in, select a network by name from the drop down list in the lower left of the screen. "Network A" through "Network F" roughly correspond to the six networks depicted on p. 280 of the article (you may need to move the nodes around on "Network C" to see the resemblance). "Empty 10" and "Empty 20" are generic unconnected networks that you can use to experiment and see how structure affects exchange behavior in this model.

You can move nodes around by dragging them. To connect a pair of nodes, click on the first (the border and label will turn red when it's selected) and then shift-click on the second. The same procedure will disconnect nodes as well. The "Exchange Size To Add" radio buttons allow you to add more profitable exchange opportunities (opportunities to exchange 24 units) and less profitable ones (opportunities to exchange 8 units).

The Step button allows you to step through a single stage of the simulation.

If a pair of nodes completes an exchange, the nodes will darken, and a green arrow will appear between them indicating the size and direction of flow of exchanged units. The table to the right will also show, for the last step, the number of units received in the last step by each actor, the number of units offered/demanded, and whether or not an deal was "closed" (corresponding to a completed exchange). Finally, the color of a node reflects the amount of units it demanded in the last round. Warmer colors indicate more units demanded, and cooler colors indicate fewer units demanded.

For more information, see:

Cook, Karen S., Emerson, Richard M. and Mary R. Gillmore. 1983. The Distribution of Power in Exchange Networks: Theory and Experimental Results. American Journal of Sociology 89(2): 275-305