Asymptotic solution to a differential equation

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Discussion Overview

The discussion revolves around finding asymptotic solutions to a differential equation of the form y^{n}= F(y, \dot y, \ddot y, \dddot y,...,y^{n-1} ). Participants explore methods for determining the behavior of the solution as x approaches infinity, particularly in the context of non-linear equations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about obtaining an asymptotic solution y(x) as x approaches infinity for a complex differential equation.
  • Another participant suggests changing the dependent variable from y(x) to u(y) = y'(x) to reduce the order of the equation, emphasizing that this transformation is not u(x) = y'(x).
  • A participant questions the possibility of determining how the differential equation diverges, proposing a form y(x) ∼ x^{a} for large x and asking if there is a method to calculate the exponent a.
  • It is noted that there is no general method for determining the asymptotic behavior of non-linear differential equations, with one participant mentioning the use of dominant balance and the need to verify assumptions afterward.

Areas of Agreement / Disagreement

Participants express differing views on the methods available for analyzing asymptotic behavior, with no consensus on a general approach for non-linear equations. The discussion remains unresolved regarding the specific techniques that can be reliably applied.

Contextual Notes

Limitations include the absence of a general method for non-linear differential equations and the reliance on assumptions about dominant balance and behavior forms, which may not hold universally.

eljose
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if we have the equation:

y^{n}= F(y, \dot y, \ddot y, \dddot y,...,y^{n-1} )

where F can be a very difficult expression in the sense that can be non-linear and so on..my question is ¿how could we get an asimptotyc solution
y(x) with x--->oo of the differential equation...thanks.
 
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and there is no form to know how the differential equation diverges?..for example let,s suppose that for big x y(x) \sim x^{a} where a is a real and positive exponent then my question is if there would be any way to calculate a..thank you.
 
eljose said:
and there is no form to know how the differential equation diverges?..for example let,s suppose that for big x y(x) \sim x^{a} where a is a real and positive exponent then my question is if there would be any way to calculate a..thank you.


There's no general method for working out the asymptotic behavior of non linear differential equations. When it is non linear you're on your own. We usually assume a dominant balance and afterwards check it out, or we assume a behavior as you did. Your "a" can be calculated substituting your expression (if suitable) in the differential equation.
 

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