3x3 similar matrices defined by characteristic and minimal polynomials

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Discussion Overview

The discussion revolves around the conditions under which two 3x3 matrices are considered similar, specifically focusing on the relationship between their characteristic and minimal polynomials. The scope includes theoretical aspects of linear algebra and matrix theory.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the sufficiency of the characteristic and minimal polynomials for determining similarity in 3x3 matrices, noting that this may not hold for larger matrices like 4x4.
  • Another participant introduces the concept of Jordan blocks as a relevant factor in understanding matrix similarity.
  • A different participant seeks clarification on the role of Jordan blocks in this context.
  • One participant explains that Jordan blocks are crucial for describing matrices up to conjugacy and asserts that the limited decomposition options for 3x3 matrices mean they are fully determined by their minimal polynomials.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the characteristic and minimal polynomials for determining similarity, with some supporting the idea while others raise questions about its limitations, particularly for larger matrices.

Contextual Notes

The discussion does not resolve the implications of Jordan blocks for matrix similarity, nor does it clarify the conditions under which the characteristic and minimal polynomials may fail for larger matrices.

JamesTheBond
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Why do you guys think that given two 3x3 matrices, they are similar if and only if their characteristic polynomial and minimal polynomial are equal (this reasonably fails for 4v4 matrices though)?
 
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Just consider the Jordan Blocks
 
Not exactly sure what you mean. How do Jordan blocks get involved?
 
Jordan blocks are what describe matrices up to conjugacy. In a 3x3 matrix there are very few ways to decompose as Jordan block matrices, which answers your question as to why 3x3 (and 2x2) matrices are completely determined by their minimal polynomials.
 

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