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Homework Help: Graphing a differential equation in mathematica?

  1. Apr 7, 2009 #1
    1. The problem statement, all variables and given/known data

    I'm trying to graph a first order differential equation in Mathematica but the graph doesn't seem right when compared to my txt book. I'm using NDSolve.

    The first order diff-eq is...

    dy/dt' = -cy-sin(x)+fcos(z)

    where z = omega t'

    c = 0.05
    f = 0.4
    omega = 0.7

    Time t' is the x-axis
    and dx/dt' is the y-axis

    3. The attempt at a solution

    I have...

    s = NDSolve[{\[Omega] x'[z] ==
    y[z], \[Omega] y'[z] == -c y[z] - Sin[x[z]] + f Cos[z],
    y[0] == -1, x[0] == 0}, {x, y}, {z, 0, 30}]

    Plot[Evaluate[y[z] /. s], {z, 0, 30}, PlotRange -> All]

    the graph should look akin to a cos function but the peaks are off compared to what's in my txt book.

    Any ideas?
  2. jcsd
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