Putting the magic in the machine since 1980.

Tuesday, October 23, 2007

Combinatorial Auction Model

One can visualize a combinatorial auction (with OR bids only) as a graph with two types of nodes: bids and items. Each bid node is labelled with the price of the bid and connected to all the items it is over. This is the visualization I have implemented in my combinatorial auction NetLogo model. It implements the branch-and-bounds algorithm on the branch-on-bids tree as found in my textbook.

Thursday, October 11, 2007

Iterated Equiresistance Model

A couple of years ago I built this simple NetLogo model that implements the iterated equiresistance algorithm in randomly generated exchange networks, as used by network exchange theory in Sociology. It now looks kinda dated and needs to be cleaned up but I thought I'd post it nonetheless. I'm using it in class as a demo.

Wednesday, October 10, 2007

Pareto Learning Model

I have posted a new netlogo model on pareto learning which implements the algorithms from this paper. This is a quick and dirty implementation for an in class demo. As nearly always happens when I do these, I found a slight problem in the paper. They specify two different ways in which the agents choose an action. Namely, first they say that the agents choose actions stochastically based on their expected utilities, then they say that they choose their best action and with probability epsilon choose a random action. After implementing both strategies it became clear that the second one is the one they actually used. Clearly, this was just a problem of the prose being a bit confusing (at least, for me).

It is also interesting to note how such a small change in the action choice method can have such large effects on the system's behavior. Because of this I have to say that the results from this model are not stable, thus they are not of deep significance.