Is Lambda an Eigenvalue of A in the Cayley-Hamilton Theorem Proof?

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Discussion Overview

The discussion centers around the Cayley-Hamilton theorem and the conditions under which a scalar lambda can be considered an eigenvalue of a matrix A. Participants are questioning the legitimacy of using the expression 1/(lambda*I - A) in the proof of the theorem, particularly in relation to the definition of eigenvalues.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions the legality of using 1/(lambda*I - A) if lambda is an eigenvalue of A, suggesting that this expression would not be valid.
  • Another participant challenges the assertion that lambda is an eigenvalue, arguing that it is merely a symbol and not necessarily an eigenvalue unless the entire proof is provided.
  • A participant references a document that may provide additional context or information related to the discussion.
  • One participant notes that the proof states "if lambda is not an eigenvalue of A," implying a conditional aspect to the argument.
  • Another participant asserts that lambda is an eigenvalue of A if and only if lambda * I - A is not invertible, contributing to the discussion on the definitions involved.
  • A later reply indicates a misinterpretation of an earlier post regarding the relationship between invertibility and eigenvalues.

Areas of Agreement / Disagreement

Participants express disagreement regarding the status of lambda as an eigenvalue and the implications of using the expression 1/(lambda*I - A). The discussion remains unresolved with multiple competing views on the matter.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about lambda and the definitions of eigenvalues, as well as the specific conditions under which the Cayley-Hamilton theorem is applied.

vabamyyr
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i met a proof to cayley hamilton theorem and have some questions.

It uses that lambda*I - A is invertible. But lambda is surely an eigenvalue of A and 1/(lamda*I - A) is not legit so how is it legal to use that.
 
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Writing 1/(lambda*I-A) is also not allowed.

Why is lambda an eigenvalue? Who says so? It is just a greek letter, probably representing some scalar. As it is unles you post all of the proof who can possibly say whether it is correct or not.
 
http://www.math.chalmers.se/~wennberg/Undervisning/ODE/linalg.pdf
 
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Also I have some questions on these topics
 

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The first sentence of the proof specifically states that "if lambda is not an eigenvalue of A"...
 
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I don't know about cayley-hamilton but I do know that lambda is an eigenvalue of A iff lambda * I - A is NOT invertible.
 
Hmm? What do you mean by that (in regards to this post)?
 
Ah, I misinterpreted his post. At first reading I thought he was claiming that lambda * I - A is invertible meant that lambda was an eigenvalue of A. Now I see that he was claiming lambda was an eigenvalue of A separately from that statement.
 

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