Relationship between determinant and trace

Click For Summary

Discussion Overview

The discussion revolves around the relationship between the determinant and the trace of matrices, specifically the equation det(M) = exp(tr(lnM)). Participants explore proofs for this relationship, particularly in the context of non-diagonalizable matrices and various matrix decompositions.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the applicability of the equation det(M) = exp(tr(lnM)) for non-diagonalizable matrices and seeks alternative proofs.
  • Another participant references a theorem from a book, suggesting that the logarithm may not be necessary in the context discussed.
  • A later reply clarifies that the logarithm is indeed intended in the original formulation, as per the participant's understanding.
  • Discussion includes the use of Jordan normal form and Schur decomposition as methods to approach the determinant and trace relationship, emphasizing the importance of these concepts in Lie group theory.
  • There is a caution raised about using the logarithm form due to the fact that not all matrices possess a logarithm.

Areas of Agreement / Disagreement

Participants express differing views on the necessity of the logarithm in the determinant-trace relationship, and there is no consensus on the best approach for non-diagonalizable matrices.

Contextual Notes

Some assumptions regarding matrix properties and the applicability of certain decompositions are not fully explored, and the discussion does not resolve the question of whether the logarithm is essential in all cases.

krishna mohan
Messages
114
Reaction score
0
Hi...

We have all seen the equation det(M)=exp(tr(lnM)). I was taught the proof using diagonalisation. I was wondering if there was a proof for non-diagonalisable matrices also.
 
Physics news on Phys.org
Theorem 2.11, page 36. (And I don't think that logarithm is supposed to be there).
 
Thanks...:smile: ...the way I have written it, the logarithm is supposed to be there...
 
Ah, I see it now. The left-hand side in the book is det(exp(M)), not det(M).
 
The book by Hall (linked above) uses the decomposition into diagonalisable + nilpotent which is very important in Lie group theory. As slightly more direct approach is to use http://en.wikipedia.org/wiki/Jordan_normal_form" .

Schur decomposition: an arbitrary matrix M decomposes as QUQ-1 where U is upper-triangular and (therefore) has the eigenvalues of M on its diagonal.

det(exp(M)) = det(exp(QUQ-1)) = det(Q exp(U) Q-1) = det(exp(U)) = ∏i exp(λi) = exp(∑λi)

exp(tr(M)) = exp(tr(QMQ-1)) = exp(tr(MQ-1Q)) = exp(tr(M)) = exp(∑λi)

btw, in general it is best to not use the logarithm form - because not all matrices will possesses a logarithm.
 
Last edited by a moderator:

Similar threads

  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
Replies
1
Views
3K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K