How to Solve a Homogeneous System with Norm Constraint?

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Discussion Overview

The discussion revolves around solving a homogeneous system of equations represented as A\mathbf{x}=0, with an additional constraint that the norm of the vector \mathbf{x} equals one. The matrix A is specified to be symmetric, but its relevance is questioned. The conversation explores methods for finding solutions, particularly focusing on the implications of the trivial solution.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant inquires about methods involving eigenvalues to solve the system A\mathbf{x}=0 under the norm constraint.
  • Another participant suggests a straightforward approach of first solving Ax=0 and then applying the norm constraint to the solutions.
  • A concern is raised regarding the trivial solution x=0, which is not desired by one participant.
  • There is a question about whether x=0 constitutes the entire solution set for the system, indicating uncertainty about the existence of non-trivial solutions.
  • One participant expresses a desire to explore the existence of other solutions beyond the trivial one and to identify those that meet the norm constraint.
  • A suggestion is made to utilize linear algebra techniques to find all solutions before applying the norm constraint.

Areas of Agreement / Disagreement

Participants express differing views on the existence of non-trivial solutions to the homogeneous system, with some uncertainty about the implications of the trivial solution. The discussion remains unresolved regarding the methods and outcomes for finding solutions that satisfy the norm constraint.

Contextual Notes

There is a lack of clarity on the completeness of the solution set for Ax=0 and the specific methods to be employed, particularly concerning the role of the symmetric nature of matrix A.

mnb96
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Hello,
how would you solve an homogeneous system of the form [itex]A\mathbf{x}=0[/itex], with the constrain [itex]<\mathbf{x},\mathbf{x}>=1[/itex]. The matrix A is symmetric, but I don't know if it matters.
There should be a method involving eigenvalues, but strangely enough, I can't find it in any book.
Thanks!
 
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Why not just do the most straightforward thing? First solve Ax=0. Then among its solutions, solve <x,x>=0.
 
The problem is that Ax=0 has a trivial solution which is x=0, and I am not interested in that.
 
If x=0 is entire solution set to Ax=0, then what does that say about the solution set to your original problem?
 
actually I don't know if x=0 is the entire solution set for the system. Hopefully it is not. I am interested in figuring out whether there are other solutions or not. and eventually find them.
 
mnb96 said:
I am interested in figuring out whether there are other solutions or not. and eventually find them.
Then do that -- use your linear algebra to find all of them.

Then once you know all of them, you can find which of them satisfy your constraint.
 

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