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Homework Help: Second-order Coupled O.D.E.s with constant coefficients

  1. Feb 11, 2009 #1
    1. The problem statement, all variables and given/known data

    I am trying to solve a system of two coupled ODEs. I am interested in an analytic solution if that is possible. I know it will be messy.

    [tex]\frac{\partial^2 U_1}{\partial x^2}+a_1\frac{\partial U_1}{\partial x^2}+b_1 U_1 = c_1 U_2[/tex]

    [tex]\frac{\partial^2 U_2}{\partial x^2}+a_2\frac{\partial U_2}{\partial x^2}+b_2 U_2 = c_2 U_1[/tex]

    3. The attempt at a solution

    I have attempted a few methods although I haven't pursued them too hard as I don't want to head down the wrong path. I found that a Laplace transform was too hard to invert. I tried to represent it as a system of 4 first order equations however the inversion was very very messy. Finally, the method I was thinking of employing was to treat the U_2 in the first equation as an arbitrary function and then exploiting the symmetry to find a solution of U_1/U_2 in terms of something in the form of:

    [tex]U_{1,2}=... + \int^x_{x_0} U_{2,1}(\eta)e^{(x-\eta)k}d\eta[/tex]

    , where k is a variable in terms of a_1 and b_2. I do not know if this will work and have not done much in this area.

    Does anyone have any suggestions as I am beginning to feel a bit out of my depth. Thanks.
  2. jcsd
  3. Feb 11, 2009 #2

    Tom Mattson

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    Solve the first equation for [itex]U_2[/itex] and plug it into the second equation.

    Why is there a "[itex]\partial x^2[/itex]" in the second term of the left hand side of each equation?
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