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A question about Green's function

  1. Jan 23, 2015 #1
    There is a second order nonhomogeneous equation of motion with nonzero initial condition given at ##t=-\infty##:
    ##D^2 y(x)=f(x)## with ##y(-\infty)=e^{-i x}##
    where I have used the shorthand notation ##D^2## for the full differential operator. Also I have the two solutions ##y_1(x)## and ##y_2(x)## to the homogeneous equation with ##y_1(x \to -\infty) \approx e^{-ix}## and ##y_2(x \to -\infty) \approx e^{ix}##. So how do I construct the particular solution using ##y_1(x)## and ##y_2(x)##?

    I know Green's function can be constructed using the two homogeneous solutions. So the naive solution I got is
    ##y(x)=y_1(x)+\int^x_{-\infty} dx' G(x,x')f(x')## with
    ##G(x,x')=\frac{y_1(x)y_2(x')-y_2(x)y_1(x')}{W(y_2(x'),y_1(x'))}##.

    Is it wrong? since I get some ridiculous result (divergence) when I use this solution to do calculation, because the lower bound is ##-\infty##.
     
  2. jcsd
  3. Jan 26, 2015 #2
    Where are you getting this out of curiosity? There are other ways to obtain the Green's function, at least.
     
  4. Jan 26, 2015 #3
    Actually I obtained this expression from the approach of variation of parameters. It plays the role of Green's function in this case.
     
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