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"# Infectious Diseases\n",
"\n",
"Consider a simple disease that follows these simple rules:\n",
"\n",
"* if you have it, then you always have it\n",
"* if you come \"in contact\" with someone who has it, then you get it\n",
"\n",
"Sounds like zombies?\n",
"\n",
"What would happen? How can we model this world?\n",
"\n",
"## Simulation\n",
"\n",
"First, we must identify the objects we wish to model. Possibilities include: \n",
"\n",
"* people\n",
"* world\n",
"* disease\n",
"\n",
"First, let's consider what properties a person should have:\n",
"\n",
"* position in the world\n",
"* whether it is carrying the disease or not\n",
"* direction heading (vector, velocity on x and y)\n",
"\n",
"Also, what actions must a person be able to do:\n",
"\n",
"* move in the world\n",
"* draw itself\n",
"\n",
"We might want to add other methods, but it needs to at least support those.\n",
"\n",
"## Person\n",
"\n",
"So, let's put together a person class. It might look something like:\n",
"\n",
"```java\n",
"class Person {\n",
" int x;\n",
" int y;\n",
" int vx;\n",
" int vy;\n",
" int carrying; // zero - not carrying disease; 1 - carrying disease\n",
" \n",
" Person(int x, int y) {\n",
" this.x = int(x);\n",
" this.y = int(y);\n",
" this.randomizeDirection();\n",
" this.carrying = 0;\n",
" } \n",
" ...\n",
"}\n",
"```\n",
"\n",
"Like the termites, instead of having them bounce off of the walls (like a ball simulation) we will instead have them \"wrap\" around (like a [torus](https://en.wikipedia.org/wiki/Torus)). For example, if a person goes too far to the left, it will wrap around to the right, and instantly appear there. Likewise, if a turtle goes below 0 or above height, then it wraps back around. Thus, we implement an infinite, repeating surface.\n",
"\n",
"This putting it all together might look like the following. \n",
"\n",
"Note:\n",
"\n",
"* people are represented by ovals. \n",
"* people turn green when they are infected"
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"People [] person; // the array of people; we'll decide how many later\n",
"int RADIUS = 5; // distance that we can sense a wood chip\n",
"\n",
"class Person {\n",
" int x;\n",
" int y;\n",
" int vx;\n",
" int vy;\n",
" int carrying; // zero - not carrying disease; 1 - carrying disease\n",
" \n",
" Person(int x, int y) {\n",
" this.x = int(x);\n",
" this.y = int(y);\n",
" this.randomizeDirection();\n",
" this.carrying = 0;\n",
" }\n",
" \n",
" void draw() {\n",
" if (this.carrying == 0) {\n",
" fill(128, 0, 0);\n",
" } else {\n",
" fill(0, 255, 0);\n",
" }\n",
" ellipse(this.x, this.y, 10, 10);\n",
" }\n",
" \n",
" int get_x(int delta) {\n",
" int dx = this.x + delta;\n",
" if (dx >= width)\n",
" dx -= width;\n",
" if (dx < 0)\n",
" dx += width;\n",
" return dx;\n",
" }\n",
" \n",
" int get_y(int delta) {\n",
" int dy = this.y + delta;\n",
" if (dy >= height)\n",
" dy -= height;\n",
" if (dy < 0)\n",
" dy += height;\n",
" return dy;\n",
" }\n",
" \n",
" void step() {\n",
" this.x = this.get_x(this.vx);\n",
" this.y = this.get_y(this.vy);\n",
" }\n",
" \n",
" void randomizeDirection() {\n",
" this.vx = 0;\n",
" this.vy = 0;\n",
" while (this.vx == 0 && this.vy == 0) {\n",
" this.vx = floor(random(3)) - 1;\n",
" this.vy = floor(random(3)) - 1;\n",
" }\n",
" }\n",
" \n",
" float distance(Person person) {\n",
" return sqrt( pow(this.x - person.x, 2) + pow(this.y - person.y, 2)); \n",
" }\n",
" \n",
" void move() {\n",
" if (this.carrying == 1) {\n",
" if (random() < 1.0) { // 10% of the time, change directions\n",
" this.randomizeDirection();\n",
" }\n",
" } else {\n",
" if (random() < .01) { // 10% of the time, change directions\n",
" this.randomizeDirection();\n",
" }\n",
" }\n",
" this.step();\n",
" // carrying a disease\n",
" if (this.carrying == 1) { \n",
" // find people within radius, and infect them\n",
" // some percentage of time\n",
" for (int p = 0; p < people.length; p++) {\n",
" if (this.distance(people[p]) < RADIUS) {\n",
" people[p].carrying = 1;\n",
" }\n",
" }\n",
" } \n",
" }\n",
"}\n",
"\n",
"void setup() {\n",
" size(500, 250); // the world\n",
" people = new Person[500]; // start termites\n",
" for (int i =0; i < people.length; i++) {\n",
" people[i] = new Person(random(width), random(height));\n",
" }\n",
" // How many to infect initially?\n",
" people[0].carrying = 1;\n",
"}\n",
"\n",
"void draw() {\n",
" background();\n",
" noStroke();\n",
" // Move the termites:\n",
" for (int i =0; i < people.length; i++) {\n",
" people[i].move();\n",
" people[i].draw();\n",
" } \n",
"}"
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