Green's Function for Linear ODE

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SUMMARY

The discussion focuses on finding the Green's function for the linear ordinary differential equation (ODE) given by $$f''(x) + \cos^2 a f(x) = 0$$ with boundary conditions $$\pm f'(x) + \cos a \cot a f(x)|_{x=\pm x_0(a)}=0$$, where $$x_0(a) = \sec a\arcsin(\cos a)$$. The proposed solution $$f(x) = \cos(\cos a (x + x_0)) + \cot a \sin\left(\cos a (x + x_0)\right)$$ satisfies the boundary conditions, yet the method of variation of parameters fails to construct the Green's function. The user seeks guidance on how to proceed with constructing the Green's function under these circumstances.

PREREQUISITES
  • Understanding of linear ordinary differential equations (ODEs)
  • Familiarity with Green's functions in the context of ODEs
  • Knowledge of boundary value problems and their conditions
  • Proficiency in the method of variation of parameters
NEXT STEPS
  • Research the construction of Green's functions for linear ODEs with non-standard boundary conditions
  • Study the method of undetermined coefficients as an alternative to variation of parameters
  • Explore the implications of parameter $$a$$ on the behavior of the solution
  • Investigate numerical methods for approximating Green's functions in complex scenarios
USEFUL FOR

Mathematics students, physicists, and engineers dealing with linear ordinary differential equations and boundary value problems, particularly those interested in advanced techniques for constructing Green's functions.

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Homework Statement


Find the Green's function for
$$f''(x) + \cos^2 a f(x) = 0;\\
\pm f'(x) + \cos a \cot a f(x)|_{x=x_0(a)}=0$$
where ##a## is a parameter and ##x_0## is defined as
$$x_0(a) = \sec a\arcsin(\cos a)$$.

Homework Equations


Standard variation of parameters

The Attempt at a Solution


A solution to the ODE is $$f(x) = \cos(\cos a (x + x_0)) + \cot a \sin\left(\cos a (x + x_0)\right)$$
But this solution satisfies both boundaries. In this case, how do you construct the Green's function since variation of parameters fails?
 
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I think someone commented but then deleted their comment, because I received an email but now cannot see their response. Anyways, I mistyped the boundaries, which are at each endpoint:
$$
\pm f'(x) + \cos a \cot a f(x)|_{x=\pm x_0(a)}=0$$

Sorry for the confusion.
 

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