1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need help on setting up an equation of population

  1. Sep 29, 2010 #1
    1. So for my computer science course I was given the homework on how to write a program on population growth. The serious dilemma is how to set up the equation. Here are the variables that are given to me:

    J = original number of Jackalopes (the imaginary animal that my teacher used)
    Y = generation (no specific unit of time)
    P = new population after each generation
    b = born percentage each generation (3% or 0.03)
    d = death percentage each generation (1% or 0.01)

    Example: J = 40 Jackalopes
    Y = 100 generations
    P = new population of 291 Jackalopes after 100 generations

    2. The most relevant equation is population growth, which involves exponential functions. the equation looks like

    X = X0ert
    X0 is the original population
    r is the net rate of growth
    t is time

    The big problem is I can't use exponential functions, because I need to truncate the results and using exponential functions don't give the answer that my teacher is looking for.

    3. Here is the attempted solution I came up with:

    P = J + (J(0.03-0.01))Y

    unfortunately my answer is way off. I recognize the pattern when I attempted to do the equation, but I don't know how to set it up. Please help me!
  2. jcsd
  3. Sep 29, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    After one generation,

    P(1) = J + (b-d)J = (1+(b-d)) J

    After Y generations,

    P(Y) = (1 +(b-d))Y J.

    It's possible to derive an exponential law if we treat a continuous growth, but this formula is fine for discrete growth. If find P(100)=290, the discrepancy might be due to round off error in a computer code.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook