#
*On
Line*

## Network SIR Model

## Network SIR Model

This model is derived from the "Virus on a Network" model
included in the NetLogo model library. See Stonedahl, F. and Wilensky,
U. (2008). *NetLogo Virus on a Network model.*
http://ccl.northwestern.edu/netlogo/models/VirusonaNetwork. Center for
Connected Learning and Computer-Based Modeling, Northwestern
University, Evanston, IL. The text that follows is based on the
information distributed with that model.

The model demonstrates the spread of a virus through a network.
Although the model is somewhat abstract, one interpretation is that
each node represents a computer, and we are modeling the progress of a
computer virus (or worm) through this network. Each node may be in one
of three states: susceptible, infected, or resistant. In the academic
literature such a model is sometimes referred to as an SIR model for
epidemics.

### HOW IT WORKS

Each time step (tick), each infected node (colored red) attempts to
infect all of its neighbors. This spread is visualized with
magenta-colored links. Susceptible neighbors (colored green) will
be infected with a probability given by the
**VIRUS-SPREAD-PROB** slider. This might correspond to the
probability that someone on the susceptible system actually executes
the infected email attachment. Resistant nodes (colored blue) cannot
be infected. This might correspond to up-to-date antivirus software and
security patches that make a computer immune to this particular virus.
Infected nodes are not immediately aware that they are infected. Only
every so often (determined by the
**VIRUS-CHECK-FREQ** slider) do the nodes check whether they are
infected by a virus. This might correspond to a regularly scheduled
virus-scan procedure, or simply a human noticing something fishy about
how the computer is behaving. When the virus has been detected, there
is a probability that the virus will be removed (determined by the
**RECOVERY-PROB** slider). If a node does recover, there is some
probability that it will become resistant to this virus in the future
(given by the
**GAIN-RESISTANCE** slider).
### HOW TO USE IT

Use the **VN-OR-MOORE** switch to create a network with potential
connectivity to either the Von Neumann (red) or Moore (green)
neighborhood of each node. The Von Neumann neighborhood is limited to
the North, South East and West directions, with the Moore neighborhood
adding Northeast, Southeast, Southwest and Northwest neighbors.

Use the **CONNECTION-PROBABILITY** slider to determine the average
number of connections. Note that for a given connection probability,
more connections will be made when using the Moore neighborhood.

Click RESET to initialize the simulation. Double-clicking RESET
also reconfigures the network.

The **VIRUS-SPREAD-PROB, VIRUS-CHECK-FREQ, RECOVERY-PROB**, and **GAIN-RESISTANCE**
sliders (discussed in "How it Works" above) can be adjusted
before pressing start, or while the model is running.

richard.salter@novamodeler.com
Last modified: Fri Jul 8 13:51:18 EDT 2016