Prove Commutation Property for 2x2 Matrices D

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    Commutation Property
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Discussion Overview

The discussion revolves around proving the commutation property for 2x2 matrices, specifically that a 2x2 matrix D commutes with all other 2x2 matrices if and only if certain conditions on its elements are met. The scope includes mathematical reasoning and exploration of linear algebra concepts.

Discussion Character

  • Mathematical reasoning, Exploratory, Debate/contested

Main Points Raised

  • One participant proposes that for a 2x2 matrix D to commute with all other 2x2 matrices, it must satisfy the conditions d12 = d21 = 0 and d11 = d22.
  • Another participant suggests testing specific matrices, such as A = \(\left(\begin{array}{cc} 0 & 1 \\ 0 & 0\end{array}\right)\), to explore the commutation property.
  • A third participant mentions that the matrices forming a basis for 2x2 matrices can be used to infer properties about all 2x2 matrices.
  • There are inquiries about how to generalize the findings or prove the claims without relying on the concept of a basis.
  • One participant references Schur's lemma as a potential generalization related to the problem.
  • Another participant expresses that they have found the solution but does not elaborate on the details.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and approaches to the problem, with no consensus reached on a definitive proof or method. Some participants are exploring specific cases while others are considering broader implications.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the properties of matrices and the reliance on specific examples or concepts like basis matrices and Schur's lemma, which may not be universally understood by all participants.

Who May Find This Useful

Readers interested in linear algebra, matrix theory, or mathematical proofs may find this discussion relevant.

vdgreat
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Let D =

[d11 d12]
[d21 d22]

be a 2x2 matrix. Prove that D commutes with all other 2x2
matrices if and only if d12 = d21 = 0 and d11 = d22.

I know if we can prove for every A, AD=DA should be true, but I really don't know how to proceed from there. I tried equating elements of AD with DA but that really didnt help.

Can anyone help me with this problem. Thanks..
 
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Try particular As, like

[tex]A = \left(\begin{array}{cc} 0 & 1 \\ 0 & 0\end{array}\right),[/tex]

and see where that leads you.
 
morphism's idea is excellent. Do you see where he got it?
The matrices
[tex]\left(\begin{array}{cc}1 & 0 \\ 0 & 0 \end{array}\right)[/tex]
[tex]\left(\begin{array}{cc}0 & 1 \\ 0 & 0 \end{array}\right)[/tex]
[tex]\left(\begin{array}{cc}0 & 0 \\ 1 & 0 \end{array}\right)[/tex]
[tex]\left(\begin{array}{cc}0 & 0 \\ 0 & 1 \end{array}\right)[/tex]
form a basis for the vector space of all 2 by 2 matrices. What is true for the basis is true for all 2 by 2 matrices.
 
but how can i prove it or generalize it??
 
help with this problem

anyone?
 
Did you think about what has been posted already?
 
Which of the basis matrices I gave commute with all other matrices?
 
try to look over schur lemma... it is a generalztion of what you asked...

ciao
marco
 
for each of the above matrices, i found out that it is true. but how can i prove this without having knowledge of basis. i haven't don't it yet.
 
  • #10
i got it thanks
 

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