Rayleigh's differential equation

Click For Summary

Discussion Overview

The discussion revolves around Rayleigh's differential equation, specifically focusing on the parameter mu and its implications for numerical solutions and phase diagrams. Participants explore the nature of mu and the numerical methods for solving the equation.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant inquires about the meaning of mu in Rayleigh's differential equation.
  • Another participant describes mu as a real positive parameter, comparing it to parameters in other ordinary differential equations (ODEs) like the Bessel differential equation.
  • A participant mentions the need to numerically solve Rayleigh's DE and questions whether the value of mu should be provided.
  • It is suggested that the value of mu can be chosen freely, with a specific recommendation to use mu = 1 for numerical solutions.
  • A participant provides the rearranged form of Rayleigh's DE as a system of differential equations and discusses the challenge of computing the second derivative without an analytical description of y2.
  • There is a query regarding the application of the classic Runge-Kutta method and whether intermediate values should be numerically approximated.

Areas of Agreement / Disagreement

Participants generally agree on the nature of mu as a parameter and the approach to numerical solutions, but there are unresolved questions regarding the specifics of the numerical method and the handling of intermediate values.

Contextual Notes

The discussion includes assumptions about the numerical methods and the specific parameters used, which may not be universally applicable. There is also a lack of consensus on the best approach to compute intermediate values in the numerical method.

Physics news on Phys.org
Well, i am asked to numerically solve it and produce a phase diagram.
Should its value be given to me?
 
I guess it should, so you're free to choose any value you want: Take \mu =1 and solve it numerically.
 
You're right , it was supposed to be given.
Rayleigh's DE is y''-\mu y' + \frac{\mu (y')^3}{3} + y = 0
By rearranging it to a system of DEs, you get
<br /> y_1 = y , y_1&#039; = y_2 \\<br /> y_2&#039; = \mu y_2 - \frac{\mu (y_2)^3}{3} - y_1<br />

So i have only the derivative of y2 , i.e. the 2nd derivative of y1.
Since i don't have an analytical description of y2 , how do i compute it with specific parameters, according to the numerical method.
For example, for the classic Runge Kutta method,where f = y'
<br /> k_1 = hf(x_n,y_n) = hy_2(n)\\<br /> k_2 = hf(x_n + 0.5h,y_n + 0.5k_1) = ?<br />
I should numerically approximate the intermmediate values as well?
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K
  • · Replies 17 ·
Replies
17
Views
4K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 23 ·
Replies
23
Views
5K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K