Linear algebra square matrices

In summary, the conversation discusses the problem of proving that there are no matrices that can satisfy the equation AB-BA=identity matrix. The attempted solution involves using the trace of matrices and eventually leads to the conclusion that the equation is impossible to satisfy. The conversation also touches on the concept of trace in linear algebra.
  • #1
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Homework Statement



A and B are two matrices n X n

Homework Equations


AB-BA=identity matrix
It is critical for me to prove that the are no matrices that are capable to hold the above equation true


The Attempt at a Solution

I made several efforts.I had the idea to get the main diagonal of AB and the main diagonal of BA same and so AB-BA would gine a main diagonal foul of zeros.But this idea was not good enough...
 
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  • #2
Do you know what the 'trace' of a matrix is? Take the trace of both sides.
 
  • #3
I found the solution! :approve:
trace(AB-BA)=trace(I)
trace is linear so trace(AB) - trace(BA) = trace(I)
Easily we prove that trace(AB)=trace(BA) so we get the following equation
0= n * 1 ,n is the dimension of matrices n x n
This of course is incongruous.
 
  • #4
Dick said:
Do you know what the 'trace' of a matrix is? Take the trace of both sides.

Now i saw what you posted.I did not knew.It's my first semester at university and my first lessons of linear algebra.Professor gave that exercise only to me in order to find it myself.I did'n know what trace is ,so what i named as main diagonal ,finally is the trace(this is what i was told by the professor when i gave to him the solution)

Anyway thanks a lot:smile:
 

FAQ: Linear algebra square matrices

1. What is a linear algebra square matrix?

A linear algebra square matrix is a type of matrix that has an equal number of rows and columns. It is represented by a capital letter and contains numbers or variables. Square matrices are commonly used in linear algebra to represent systems of linear equations and perform various operations such as addition, subtraction, multiplication, and inversion.

2. What are the properties of a square matrix?

A square matrix has several properties that make it unique. These include having an equal number of rows and columns, being symmetric if it is the same when reflected along the main diagonal, being skew-symmetric if its elements change sign when reflected along the main diagonal, and being invertible if it has a unique solution when solving for its inverse.

3. How do you multiply two square matrices?

To multiply two square matrices, the number of columns in the first matrix must be equal to the number of rows in the second matrix. The resulting matrix will have the same number of rows as the first matrix and the same number of columns as the second matrix. To find the value of each element in the resulting matrix, you multiply the corresponding row of the first matrix by the corresponding column of the second matrix and then add the products.

4. What is the determinant of a square matrix?

The determinant of a square matrix is a scalar value that represents the scaling factor of the matrix. It is calculated by a specific formula and can be used to determine if a matrix is invertible. If the determinant is zero, the matrix is not invertible, and if it is non-zero, the matrix is invertible.

5. How is a square matrix used in real-world applications?

Square matrices have many real-world applications, including computer graphics, engineering, physics, economics, and data analysis. They are used to solve systems of linear equations, perform transformations, and analyze data. For example, in computer graphics, square matrices are used to represent the transformation of 3D objects, and in economics, they are used to model supply and demand systems.

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