Rearrange equation (solution of ODE)

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Discussion Overview

The discussion centers around the rearrangement of an equation derived from a nonlinear first order ordinary differential equation (ODE). Participants explore the feasibility of expressing the solution in terms of the variable R.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant presents the equation $$\ln(R)+\frac{mR^{n-1}}{n-1}=\bar{w}_{\infty}\xi+C$$ and seeks to rearrange it for R.
  • Another participant questions whether R(x) is the function solving the differential equation in the variable x.
  • A different participant asserts that the equation cannot be rearranged to solve for R, stating it essentially reduces to $$\ln(R^{n-1}) + mR^{n-1} = A$$ which lacks an analytic solution for R.
  • One participant clarifies that R is a function of ξ and reiterates the need to express R(ξ) explicitly.
  • Another participant confirms that there is no solution in terms of elementary functions for the equation presented.
  • A final post indicates the closure of the thread, suggesting the question has been resolved.

Areas of Agreement / Disagreement

Participants generally agree that the equation cannot be rearranged to yield R in terms of elementary functions, although the discussion reflects some uncertainty regarding the specifics of the rearrangement process.

Contextual Notes

Limitations include the lack of analytic solutions for the rearrangement of the equation and the dependence on the definitions of the functions involved.

Juggler123
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I have determined the solution to a nonlinear first order ordinary differential equation but am struggling to rearrange the result, I have that

$$\\ln(R)+\frac{mR^{n-1}}{n-1}=\bar{w}_{\infty}\xi+C.$$

How would I rearrange this equation for $$R$$?
 
Last edited:
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Do you mean that R(x) is the function that solves a differential equation in the variable x ?
 
Juggler123 said:
I have determined the solution to a nonlinear first order ordinary differential equation but am struggling to rearrange the result, I have that

$$\\ln(R)+\frac{mR^{n-1}}{n-1}=\bar{w}_{\infty}\xi+C.$$

How would I rearrange this equation for $$R$$?

You can't. What you have is essentially <br /> \ln(R^{n-1}) + mR^{n-1} = A which doesn't have an analytic solution for R^{n-1} given A.
 
Sorry I should have been more clear. I have determined the solution R(\xi), the solution is

$$\ln(R(\xi))+\frac{mR(\xi)^{n-1}}{n-1}=\bar{w}_{\infty}\xi+C.$$

I simply need to rearrange this to say R(\xi)=\cdots
 
That was clear. And what you have been told that there is no solution in terms of elementary functions.
 
The question has been asked and answered, so I'm closing this thread.
 

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