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Homework Help: Another Green function question.

  1. Mar 22, 2008 #1

    MathematicalPhysicist

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    find the eigenfunctions and eigen values of the next equation:
    [tex]d^2y/dx^2+u_n^2y=0[/tex]
    where y(0)=0=y(pi).
    Now find the green function of the above non-homogeneous equation, i.e:
    [tex]d^2G_{\lambda}(x,a)/dx^2-\lambda G_{\lambda}(x,a)=\delta(x-a)[/tex]
    where a is in (0,pi) and lambda doesnt equal the -u_n^2.


    Now here's what I did, the eigenfunction are y(x)=Asin(nx) and u_n=n.

    Now for the green function for x different than a the above equation is 0, and the ( l is the same as lambda) solution is: G(x,a)=Ae^(sqrt(l)x)+Be^(-sqrt(l)x))
    now in G(pi)=0=Ae^(2sqrt(l)pi)+B
    B=-Ae^(2sqrt(l)pi) this is for x in (a,pi] for x in [0,a) we have B=-A, then we have yet without the a:
    for x in [0,a) A(e^(sqrt(l)x)-e^(-sqrt(l)x))
    for x in (a,pi] A(e^(sqrt(l)x)-e^(2sqrt(l)pi)e^(-sqrt(l)x))
    now we need continuity at x=a, but from this we need to get that l=0, did I do something wrong in my reasoning here?

    any advice on how to amend it?
     
  2. jcsd
  3. Mar 29, 2008 #2

    MathematicalPhysicist

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    can anyone give some hint?
     
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