Reducing and increase of order and ODE

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    increase Ode
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Discussion Overview

The discussion revolves around the concepts of reducing and increasing the order of ordinary differential equations (ODEs) and whether similar techniques can be applied to partial differential equations (PDEs). Participants explore the implications of these techniques in the context of linear equations and the conditions under which they may be applicable.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether it is possible to reduce the number of equations in a system of ODEs by increasing the order of the equations.
  • Another participant suggests that certain conditions, such as linearity, must be met for techniques like separation of variables to be applicable to PDEs.
  • A different participant notes that the separability of linear equations can depend on the geometry of the situation, indicating that an equation may be separable in one coordinate system but not in another.
  • One participant provides an example of how differentiating one of the equations in a system can lead to a second-order differential equation, suggesting that multiple approaches exist for manipulating the order of equations.
  • It is mentioned that in general, n linear differential equations with constant coefficients can yield a single nth-order equation in one variable, but only one solution is necessary for practical purposes.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of reducing and increasing order in ODEs and PDEs, with no consensus reached on the conditions required for these techniques.

Contextual Notes

Limitations include the dependence on the linearity of equations and the geometry of the coordinate systems involved, which may affect the separability of equations.

Bruno Tolentino
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Two questions:

First: If is possible to reduce the order of an ODE increasing the number of equations, so, is possible do the inverse patch? In other words, is possible reduce the number of equations of a system of ODE increasing the order?

Second: This technique of reducing and increasing of order is applicable to a PDE/system of PDE?
 
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Even in with linear equations, whether or not it is separable depends upon the geometry of the situation. An equation may be separable in one coordinate system and not in another.
 
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You can certainly do that in the case where you did the opposite recently https://www.physicsforums.com/threads/system-of-ode-of-second-order.825408/ . More than one way around but if you differentiate one of the equations you will find you have enough to eliminate y and y' and finish with an 2nd order d.e. in x. Then with no added effort with one in y too. In general n linear d.e.s with constant coefficients like that you can get one n'th order one in one variable. In fact you can get n of them. But if you are interested in solutions you only need to get one, and the other solutions are merely a renaming of terms.
 
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