Applying Boundary Conditions in Homogeneous ODE Problems

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Homework Help Overview

The discussion revolves around applying boundary conditions to a homogeneous ordinary differential equation (ODE) problem involving eigenvalues and eigenfunctions. The specific ODE is of the form {u}''(x) + 2{u}'(x) + λu(x) = 0, with boundary conditions u(0) = 0 and u(1) = 0. Participants are exploring the implications of different values of λ and the corresponding general solutions.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the general solution forms, including exponential and hyperbolic functions, and how to apply boundary conditions correctly. There are questions about the implications of setting coefficients to zero based on boundary conditions and whether certain assumptions about the functions can be made.

Discussion Status

There is an ongoing exploration of how to apply boundary conditions effectively, with some participants suggesting specific approaches while others express confusion about the implications of their results. Multiple interpretations of the boundary conditions and the behavior of the solutions are being considered.

Contextual Notes

Some participants have noted potential typos or misunderstandings regarding the notation used in the problem, particularly concerning the variable λ and its dependence on x. The discussion also highlights the challenge of determining the coefficients in the general solution based on the boundary conditions.

  • #31
Fantastic. Didn't see that at all. Thanks very much!

For \lambda=1 \Rightarrow u(x)=e^{-x}[Ax+B]
So u(0)=0 \Rightarrow B=0 and u(1)=0 \Rightarrow A=0 and therefore u(x)=0

For \lambda>1 \Rightarrow u(x)=e^{-x}[A\cos (\sqrt{\lambda-1})x+B\sin (\sqrt{\lambda-1})x]
So u(0)=0 \Rightarrow A=0 and u(1)=0 \Rightarrow either B=0 or \sin (\sqrt{\lambda-1})=0 \Rightarrow (\sqrt{\lambda-1})=n\pi

So the eigenvalues are \lambda =1+\pi^{2}n^{2}
And the eigenfunctions are u(x)=Be^{-x}\sin (n\pi x)

All correct?
 
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  • #32
Yes, it looks correct:smile:

ehild
 
  • #33
Great. Thanks so much for all your help!
I'm pleased to put this one to bed and come out having cleared some things up.
Cheers!
 

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