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This is a model of distribution of resources through a network. For demonstration purposes, we use laws for directing agents in Alaska to distribute resources during emergencies. Hit Setup and then hit Distribute and see resources flow through this directed network.

Each node shares its resources with its neighbors in the network. If you set "resources distributed equally" then the amount of shared resources is divided equally and sent along each of the outgoing links from each node to each other node. If a node has no outgoing links, then it doesn't share any of it's value; it just accumulates any that its neighbors have provided via incoming links.

The size of each node shows how much value of resources that node has, where the area of the node is proportional to its value. The brightness of a link represents how much value just flowed through that edge.

Note that because it is a directed network, some nodes may receive resources but give none back, e.g. the public only receives resources.

We can setup many more specific flow networks, e.g. money during a specific type of emergency. This flow network is simplified in many ways for demonstration purposes. (One simplifying assumption is equal initial resources and equal outflow rates per neighboring node.)

You can set "more detailed networks" to see administrative agencies broken down into more specific categories.

Yet this demonstration shows an essential nature of network flows. Here we show that resources flow from agencies and officials to the public, doctors, and employers.

HOW TO USE IT

Choose the type of "network" that you want to model, either "all resources" or only "money resources only".

Choose the initial distribution of resources in the network, either "equal" distribution, in which case all nodes start with the or "distributors only"--distributors are those with outlinks.

To create the network and initial resources, press SETUP.

Press the DISTRIBUTE button to run the model.

After hitting DISTRIBUTE You can click on any node to give it more value, or move any node by dragging it.

After running the model with all nodes present, you can try deleting a central node (then hit setup) and try running the model again to see if there is difference in the flow. You can also delete a link at random to see the effects. Notice that there is some redundancy in the pathways which gives the flow resilience, meaning there are backup pathways of flows which helps make the distribution less vulnerable to "deletions" of nodes.

DIFFUSION-RATE indicates how much "value" each node shares with its neighbors during a given time step. The default is 1% so the distribution is slow enough for you to see the process. At each "tick" 1% of resources are distributed to outlinks as described earlier.Changing this to a higher level only speeds up the distribution.


CREDITS AND REFERENCES

Chris Keane developed this specific model, based on work with Patt Sweeney et al.

He borrows a procedure developed by Stonedahl, F. and Wilensky, U. (2008). NetLogo Diffusion on a Directed Network model. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL. Netlogo: Copyright 2008 Uri Wilensky. All rights reserved.