an agent-based model
ePROBE (exploring Policies for Recycling Of BiowastE) is an agent-based model aimed at investigating the impact of different policies and different policy combinations on the development of the bio-waste industry. The focus is on two policies: (i) the funding of facilitators to help create symbiotic links between companies and (ii) the role of a financial instrument.
In the simulation, the 'agents' are companies (sometimes referred to as firms). These companies have a contact network, where a contact is another company that they are aware of but have no formal contract with. They also have a network of contracts with companies, either a contract to supply material to another company or a contract to obtain material from another company. In the simulation, the network of 'friends' is shown in red and the network of contracts is shown in either blue or black - black means that the contract is for organic waste, blue is for waste oil.
Why should I use an agent-based model?
This model is just one example of agent-based modelling, an approach to developing simulations of policy processes which places the heterogeneity of actors, and their interaction with each other and the policy landscape, at the center of the modelling process. You can read more about agent-based modelling here.
The model interface:
These instructions allow you to download and run the model. This demonstration is intended to help you understand what an agent-based model is, how it works, and how the approach may of use in your topic or problem area. If you think an agent-based model of the food supply chain during food incidents is closer to your interests, you may prefer to look at the INFOrM model.
First, you should download and open the model. To do this you will need to download 'NetLogo', the program in which the model runs. It is important that you download the correct version of NetLogo - version 5.0.5. To download NetLogo 5.0.5, go to https://ccl.northwestern.edu/netlogo/ and follow the instructions.
Once you have done this, download the model here (you must use 'right click and save as', using '.nlogo' as the file type), and open it in NetLogo.
Controlling the model
First leave the sliders at their pre-set values.
- Click on setup. You should see a number of green circles and a large green square appear. These represent producers of waste. The number of green circles depends on the value of the slider Number-of-wasteproducers.
- Click on go once. This runs the model forward one day. You should see that some new coloured circles appear. If there is enough waste oil in the system then a blue circle representing a biodiesel plant will appear. Either an AD plant (red circle) or a composter (black circle) will also appear. Red links representing initial contacts between waste producers and waste processors will also appear.
- Click on go once again. This runs the model forward one more day. You should see some blue and black arrows form. The blue arrows represent the flow of waste oil, the black arrows represent the flow of organic waste. Note that the amount of oil waste and organic waste going to landfill drops as shown in the graph labelled ‚ÄúWaste to landfill‚Äù ‚Äì this is less easy to see in the case of organic waste. Since there is far less waste oil than organic waste in the system, in order to fit both on the same graph the scale on the graph shows tonnes of waste oil but tens of tonnes of organic waste.
- You could keep on clicking on go once to keep stepping the model forward one day. But instead, try clicking on go forever. You should see the model now keeps running. It will keep running until you click on go forever again.
- You can look at the properties/variables of any agent or link by pointing the mouse at the agent or link and right clicking.
Exploring the model's behaviour
The role of initial-contacts and contact-rate
- Set the initial-contacts and the contact-rate to 0. Click on setup and then go forever. What happens?
You should see that although companies come into existence (they‚Äôve identified that there is waste available) since no contacts are made, no material exchanges occur and, ultimately, the waste processing companies go bust.
- Set the initial-contacts to 4 and leave the contact-rate at 0. Click on setup and then click on go once a few times. What happens?
You should see that companies now come into existence and establish 4 contacts. They develop no new contacts over time and material exchanges only occur within the contact network.
- Set the initial-contacts to 0 and set the contact-rate to 15. Click on setup and then click on go once a few times. What happens?
You should see that new companies start by knowing no-one. Every second day they add one new contact to their network. (A contact-rate of 15 means 15 new contacts each month).
Organic waste market dynamics
Set the sliders as follows:
Click on setup and then go forever. Let the model run. What happens over time? To the daily profit of the composters? To the daily profit of the AD plants? To the mean price of organic waste? (If you want the simulation to run faster, move the slider in the grey bar at the top from normal speed to the right).
Once the mean price for organic waste has reached an approximately steady value (about 15000 days - NB: it may take several minutes for the model to get this far), pause the run by clicking on go forever. Change the slider labelled ROCs-incentive from 14 to 5. What happens?
ePROBE is licensed under a Creative Commons Attribution 4.0 International License.
Our Approach: Understand the system
Tools: INFOrM ABM
Case study: Humber