# Better to be Prepared: When Zombies Attack!

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I remember that I was playing Resident Evil, after everybody sleep, in fear for hours. Although I really don’t like the “zombie” idea, it’s a popular phenomena that people want to be prepared for a zombie outbreak. I am not sure about its likelihood, but obviously it’s popular among generations and some people may be happy if it really happens.

Well, what is the deal with zombies in an Operations Research blog? Here it comes: I read a paper about mathematical modelling of zombie outbreak. ‘When zombies attack!: mathematical modelling of an outbreak of zombie infection‘ [1] is written by Munz et. al is an interesting paper that cites movies and popular PC games such as Resident Evil, Dead Rising, Shaun of the Dead, 28 Days Later and Dawn of the Dead. (Citing PC games sounds cool for a research )

In their paper, there are three classes of people: Susceptible (S), Zombie (Z) and Removed (R). Later they also used Infected (I) and Quarantine (Q) classes. These classes have relations and balance equations in different scenarios, for instances victims stay a period of time as infected, and for people who are in quarantine, cure can be applied. That is good to hear ‘cure zombiness’ even if it’s only a mathematical model. For each model they are finding an equilibrium that represents long-run behavior of the system.

There is a simple simulation tool [2] that is independent of the paper, where you can observe a possible zombie outbreak. Zombies are represented in gray color and eventually everyone in the city becomes zombie. Similar to this simulation, unfortunately, in most of the scenarios in the paper, all individuals eventually becomes zombie as well. As they stated in conclusion, the only survival method is decreasing number of zombies by attacking them. They said

While aggressive quarantine may eradicate the infection, this is unlikely to happen in practice. A cure would only result in some humans surviving the outbreak, although they will still coexist with zombies. Only sufﬁciently frequent attacks, with increasing force, will result in eradication, assuming the available resources can be mustered in time

A figure from the paper that shows population values of two classes in long time, where treatment is used.

We discussed the public effects of zombie outbreak and survival chances. Let’s focus on a simple problem: What will you do if zombie outbreak happens? This time your objective is maximizing likelihood of your survival. Neuroscientist Bradley Voytek prepared a simple “survival infographic” by using cognitive problems of zombies: (also check here)

Well, if you want to experience a zombie outbreak yourself, here is a nearby chance for you: The Walking Dead Escape (Philadelphia on April 21 and San Diego on July 19,20) You can join the escape as a zombie, a survivor or just as an observer!

I enjoyed the paper and find it interesting. What do you think? Do you have any other ideas to fight against zombies?

[1] Munz, Philip, et al. “When zombies attack!: mathematical modelling of an outbreak of zombie infection.” Infectious Disease Modelling Research Progress 4 (2009): 133-150.

[2] “Zombie Infection Simulation V2.3 – The Original.” Zombie Infection Simulation. N.p., n.d. Web. 05 Apr. 2013.

Sertalp Bilal Çay

PhD Candidate and Teaching Assistant in Industrial and Systems Engineering Department at Lehigh University. Researcher on Conic Optimization, Inventory Theory, Supply Chain Management and Simulation. Blog: sertalpbilal.com