Help getting started with this differential equation

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Discussion Overview

The discussion centers around solving the differential equation ∂²Φ/∂s² + (1/s)∂Φ/ds - C = 0, where s is a radial coordinate and C is a constant. Participants are exploring methods for finding a general solution, including the potential use of the method of undetermined coefficients.

Discussion Character

  • Homework-related, Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on how to start solving the differential equation and questions whether the method of undetermined coefficients is appropriate.
  • Another participant suggests substituting ##\Psi=d\Phi/ds## to transform the equation into a first-order equation, indicating that an integrating factor could be used for solving it.
  • A different participant reformulates the original equation into a specific form, $$\frac{1}{s}\frac{\partial}{\partial s}\left(s\frac{\partial \phi}{\partial s}\right)=C$$, which may provide a different perspective on the problem.
  • One participant questions the use of partial derivative symbols given that the equation involves only a single variable, s.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the best approach to solve the equation, and multiple methods and interpretations are being discussed.

Contextual Notes

There are unresolved questions regarding the appropriateness of the method of undetermined coefficients and the implications of using partial derivatives in the context of a single variable.

Daniel Sellers
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TL;DR
I have a fairly simple non-homogeneous second order ODE to solve but I can't seem to get started with it.
I need to solve

2Φ/∂s2 + (1/s)*∂Φ/ds - C = 0

Where s is a radial coordinate and C is a constant.

I know this is fairly simple but I haven't had to solve a problem like this in a long time. Can someone advise me on how to begin working towards a general solution?

Is the method of undetermined coefficients the correct approach?

Thanks very much.
 
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Substituting ##\Psi=d\Phi/ds## turns your equation into the first order equation ##\Psi'(s)+\frac{1}{s}\Psi(s)=C##. You should be able to do this with an integrating factor.
 
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The equation is the same as $$\frac{1}{s}\frac{\partial}{\partial s}\left(s\frac{\partial \phi}{\partial s}\right)=C$$
 
Last edited:
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Is there a reason for the partial derivative symbols when there is only the single variable s?
 
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