How to detect redundant equation from a system of nonlinear equation?

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Discussion Overview

The discussion revolves around the detection of redundant equations within a system of nonlinear equations, specifically focusing on the concept of linear independence among these equations.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant inquires about methods to determine if a system of nonlinear equations is linearly independent, suggesting that one equation should not be representable by others.
  • Another participant mentions that there is no general method for identifying redundant equations, although the Jacobian may provide some assistance for differentiable nonlinear equations.
  • A further inquiry is made regarding the use of the Jacobian matrix to identify redundancy, with skepticism expressed about the reliability of the Jacobian matrix having redundant rows to imply redundancy in the original equations.
  • A reference is made to a source that states the Jacobian being zero throughout an open set indicates functional dependence among the functions, emphasizing that conclusions cannot be drawn from the Jacobian vanishing at a single point.
  • There is a mention of algebraic geometry as a field that addresses systems of polynomials, suggesting its relevance to the discussion but noting its abstract nature.

Areas of Agreement / Disagreement

Participants express differing views on the reliability of the Jacobian in determining redundancy, and there is no consensus on a general method for identifying redundant equations in nonlinear systems.

Contextual Notes

Limitations include the dependence on the properties of the Jacobian and the need for open sets to draw conclusions about functional dependence, which may not apply to all cases.

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How to detect redundant equation from a system of nonlinear equation?
It means how to find out a system of nonlinear equation is "linear independence"?
One equation from the system can not be represented by the others in the system of nonlinear equation.
 
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Welcome gohkgohkgohk .
I'm afraid there's no general method of spotting a redundant equation from a set. The Jacobian helps a liitle if you have differentiable non-linear equations.
 
Hi Eynstone, could you share more details on how to determine the redundant equation using Jacobian? My suspection is even its Jacobian matrix has redundant rows, the non-linear equation system may not have redundant equations.
 
I checked the section on functional dependence from Gerald Folland's Advanced Calculus.

There it says, if you consider on open set U, then

Jacobian is zero throughout U if and only if the functions have some (possibly various) functional dependence(s) throughout U.

So it's not enough for the Jacobian to vanish at a single point, calculus needs an open set to draw conclusions. To deal with single points, I think is part of the practicality of the subject algebraic geometry, which more or less deals with systems of polynomials, as far as I know, but looks like a very abstract subject.
 
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