Zombie Infection Simulator

Yesterday evening, as I was wiling away some hours at the computer, a thought struck me. I realized that my knowledge of NetLogo has finally reached the point at which I could build something I’ve wanted to build for a long time: a simulation of a zombie outbreak. Ever since I saw the cool simulator on this page, I’ve wanted to build my own version in NetLogo, but I’ve never been competent enough to program it. Now that I’ve got some experience under my belt, I was finally able to pull it off.

Here are the basics:

• Humans show up as blue dots. They walk at a leisurely pace, and flock together with other humans.
• Panicked humans result whenever a human sees a zombie or another panicked human. Panicked humans run faster than normal ones, change directions more often, and don’t flock. If there’s nothing threatening about, and the general panic level has died down, they turn back into normal humans.
• Zombies are green. They lack any sort of intelligence and wander around randomly. If a human gets too close to them, they may attack, resulting in infection.
• Fighting humans are humanity’s only hope to resist the zombie hordes. They show up as yellow. Fighters flock together with other fighters, and also seek out any zombies nearby. They also have a rallying effect. That is, they have a tendency to make panicking humans calm and urge calm humans to fight. Sometimes, fighters break under the strain and panic, or, if there are no immediate threats, they go back to normal.

These rules are fairly simple, but I’ve been working with StarLogo and NetLogo for long enough now to know that emergence can perform feats of magic with simple rules. And I did indeed get some fascinating behavior.

As I toyed around with the simulator, I discovered the importance of scaling. With a small map and a large population, the behavior seemed to resemble that one might find in an urban setting, and as the map size increased, the behavior seemed to be more like that of a county or a small country, with the groups of humans representing cities, or something to that effect.

The first run I did for this post was an urban one with an initial human population of 300 (THIS IS SPARTAAA!!! Sorry…couldn’t help myself.)

The humans have organized into “flocks”. For some reason, there seems to be a bias that causes them to favor moving down the map, rather than in some other direction. I’m still trying to fix that particular bug.

Now the fun part begins. I cause one human to suddenly become a zombie, and the infection starts. All the people nearby start to panic, except for a small group of renegades who become fighters and start hunting down the zombies.

As the epidemic begins to grow out of control, panic spreads throughout the “city”. Groups of fighters attempt to rally the panicking citizenry, but their efforts are for naught, as the growing zombie horde continues to inspire panic.

Groups of fighters still try valiantly to keep the infection under control, but it’s already too far gone. By this point, social organization is beginning to decay.

As the situation continues to spiral out of control, social order breaks down, and humans stop forming flocks. Groups of fighters are overwhelmed on every front.

It is the end of days (well, at least the end of the “city”). There are few humans left, and those survivors are panicked and running for their lives. Note the single fighter still trying to kill zombies. Unfortunately, this is not an actual zombie movie, and so there’s pretty much no chance that a ruggedly good-looking male protagonist is going to rally a ragtag group of comic-relief-spouting survivors and save the day.

This program is incredibly fun to play with, and I’ll put it up for download as soon as I get around to it. In the meantime, I’ll do a larger run, one that represents more of a “nationwide” zombie epidemic. But since, for some reason, this simulation is pretty CPU-intensive, it’s going to take me a while to get around to running that one.

Many thanks to Kevan Davis for the inspiration for this simulation!

And, once again, many thanks to the makers of NetLogo. I know it sounds like I’m on their payroll or something, but NetLogo really does make programming multi-agent simulations pathetically simple.