Does A Have a Positive Eigenvalue Using Topology?

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SUMMARY

The discussion confirms that a 3x3 matrix A with positive real entries possesses at least one positive real eigenvalue. This conclusion is derived using Brouwer's Fixed Point Theorem, which is applicable because the positive entries indicate that the linear transformation maps the first octant to itself. By following the linear transformation with a projection, the conditions for applying Brouwer's theorem are satisfied, leading to the established result.

PREREQUISITES
  • Understanding of eigenvalues and eigenvectors in linear algebra
  • Familiarity with Brouwer's Fixed Point Theorem
  • Knowledge of linear transformations and their properties
  • Basic concepts of topology related to fundamental groups
NEXT STEPS
  • Study the application of Brouwer's Fixed Point Theorem in various mathematical contexts
  • Explore the relationship between matrix properties and eigenvalues in linear algebra
  • Learn about linear transformations and their geometric interpretations
  • Investigate the implications of positive matrices in eigenvalue theory
USEFUL FOR

Students and educators in mathematics, particularly those focusing on linear algebra and topology, as well as researchers interested in the applications of eigenvalues in various fields.

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Homework Statement



Let A denote a 3x3 matrix with positive real entries. Show that A has a positive real Eigenvalue.

Homework Equations



This is a problem from a topology course, assigned in the chapter on fundamental groups and the Brouwer fixed point theorem.

The Attempt at a Solution



I don't know where to start (besides brute force algebra, maybe).
 
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I believe that you do in fact need to use Brouwer's Fixed Point Theorem here.
 
I figured that much, if just for purely pedagogical reasons.

For a while I didn't know how to use the positive entries of the matrix, until I realized that that means that the first octant is mapped to itself by the linear transformation. Follow the linear transformation by a projection and I am set up for Brouwer.

Done!

<('-')> <(''<) <('-')> (>'-')> <('-')> <(''<) <('-')> (>'-')> <('-')> <(''<) <('-')> <('-')> (>'-')> <('-')> <(''<) <('-')>
 

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