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| Q9: | What is the logistic equation? |
| A9: | It models animal populations. The equation is x -> c x ( 1 - x) , where |
x is the population (between 0 and 1) and c is a growth constant. Iteration of |
this equation yields the period doubling route to chaos. For c between 1 and |
3, the population will settle to a fixed value. At 3, the period doubles to 2; |
one year the population is very high, causing a low population the next year, |
causing a high population the following year. At 3.45, the period doubles |
again to 4, meaning the population has a four year cycle. The period keeps |
doubling, faster and faster, at 3.54, 3.564, 3.569, and so forth. At 3.57, |
chaos occurs; the population never settles to a fixed period. For most c |
values between 3.57 and 4, the population is chaotic, but there are also |
periodic regions. For any fixed period, there is some c value that will yield |
that period. See An Introduction to Chaotic Dynamical Systems, by R. L. |
Devaney, for more information. |
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