MathBench > Population Dynamics

Stage-based Models

Compartmentalizing the students

That evening in the dining hall, Dumbledore explains his idea to the students. As he sees it, the students can be divided into three groups:

  1. Those that have never had pigeon pox, and
  2. Those that currently have pigeon pox, and
  3. Those who have gotten over pigeon pox and therefore will never get it again.

    4. Professor Snape remarks that perhaps Dumbledore should add a fourth group,
  4. Those who have died due to pigeon pox

Dumbledore counters, however, with the reminder that pigeon pox is very rarely fatal. He then waves his wand, and magically the students find that their school robes have been exchanged for brightly colored, ugly t-shirts. On each t-shirt is a large letter “S”. That’s for “susceptible”, beams Dumbledore. On every shirt except one, that is. Neville Longbottom’s shirt reads “I”, for infected

Dumbledore waves his wand again and an ornate scroll appears in his hand. He reads it off: current student body status: 599 susceptibles, 1 infected.