Solving Coupled ODEs: x(t) and y(t)

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    Coupled Odes
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Discussion Overview

The discussion centers on solving a system of coupled ordinary differential equations (ODEs) involving two variables, x(t) and y(t). Participants explore potential methods for finding solutions, including analytical and numerical approaches, while addressing the complexities introduced by the non-linear nature of the equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents the coupled ODEs and seeks methods to solve for x(t) and y(t).
  • Another participant suggests that an analytical solution may not exist due to the non-linear nature of the system and proposes linearization around the point (0,0) as a possible approach, though they express uncertainty about handling the second derivatives.
  • A different participant mentions the possibility of using numerical methods to solve the equations but notes that initial conditions are necessary for such an approach.
  • Another participant questions the stability of the system, suggesting that local analysis and linearization around critical points may reveal instability, which could affect simulations unless starting precisely at those points.

Areas of Agreement / Disagreement

Participants express differing views on the existence of analytical solutions and the stability of the system. There is no consensus on the best approach to solving the coupled ODEs, and multiple competing views remain regarding the methods to be employed.

Contextual Notes

The discussion highlights the challenges posed by the non-linear nature of the equations and the implications for stability and solution methods. Specific assumptions about initial conditions and the behavior of the system near critical points are noted but not resolved.

exmachina
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I have the following coupled ODE:

2x+y^2=d^2x/dt^2
2y+x^2=d^2y/dt^2

How would one solve for x(t), y(t)?
 
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Although I am no expert, I don't think there is an analytical solution to this differential equation. It is a non-linear system, which makes it already really difficult. One could linearize it around (0,0), however I don't know how to deal with the fact it is a second derivative instead of a first... perhaps a more skilled person can help.
 
Are you sure about the signs? this is unstable anywhere. Local analysis can help you. If you set the system
[tex]x_{1}\equiv x, x_{2}\equiv x',x_{3}\equiv y,x_{4}\equiv y'[/tex]
and then look for the critical points, where all four equations go to zero, and you linearize around those points, it turns out there is always an unstable direction, so that your simulations will crash too, unless you start exactly at the critical points ((0,0) and (-2,-2))
 

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