Is the Trace Method the Key to Proving Ab-ba=i Has No Solution?

  • Context: Undergrad 
  • Thread starter Thread starter GreenApple
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Discussion Overview

The discussion revolves around the problem of proving that the equation AB - BA = I has no solution for real square matrices A and B. Participants explore various approaches and concepts related to this problem, particularly focusing on the trace method.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Conceptual clarification

Main Points Raised

  • One participant expresses difficulty in understanding the problem and seeks input from others.
  • Another participant clarifies the problem statement, emphasizing the need to prove the non-existence of real square matrices A and B that satisfy the equation.
  • A suggestion is made that the trace could be a key tool in proving the statement, although the details of this approach are not elaborated.
  • A participant proposes a specific case using 1x1 matrices, arguing that they would commute, thus questioning the validity of the original problem.
  • Another participant responds by clarifying that real matrices can have dimensions greater than 1x1, indicating a misunderstanding of the problem's requirements.
  • One participant acknowledges the use of the trace method and questions whether it was specifically developed to address this problem.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity of the original problem, as there are differing views on the applicability of the 1x1 matrix example and the role of the trace method.

Contextual Notes

There is a lack of clarity regarding the assumptions about matrix dimensions and the implications of using the trace method. The discussion does not resolve whether the trace method definitively proves the statement.

Who May Find This Useful

Students and enthusiasts of linear algebra, particularly those interested in matrix theory and the properties of matrix operations.

GreenApple
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Hi,I am a Chinese sophomore major in software engineering.I am reading Artin's Algebrarecently and have come across this problem in 1.1,and have been trying for 4 days in vain:cry:

Give me some real thought guys,I will really appreciate it!
 
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Sorry,the problem should be this:prove AB-BA=I has no solution with realnumber where A and B are matrix
 
I suppose you mean that you want to prove that there are no real square matrices A and B such that AB - BA = I. The key to proving this: Trace.
 
It's probably way out of my area, but let's say you take a 1x1 matrix for A and a 1x1 matrix for B. Then A*B will equal B*A...because there are no additions or substractions etc inside the matrixes...and since they're both 1*1 they can be multiplied...wouldn't matrix I end up being just ?

[0]

I probably said something very stupid...but it seems to me that it follows all the question parts...it's a matrix, it's real, it's a solution...and A and B can be anything...
 
Real matrices are those matrices which have real entries. They are not necessarily 1x1.
 
Oh so you have to prove the identity for all of them? I think what I was trying to do is find one case that works. Yeah...I'm way over my head...:(
 
thanks!

Yeah,using trace works!
Another question:is trace invented just to prove this problem?I believe that a new concept usually come from a new mothod proving something.
 

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