Showing that two 4x4 matrices are similar

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In summary, the conversation is about proving the similarity of two 4x4 matrices A and B. The equation A = SBS^-1 is used to show similarity, and the student is struggling to find a non-singular invertible matrix S to satisfy the equation. They have not learned eigenvalues or eigenvectors yet and are seeking help with the problem. It is noted that S is not unique and any matrix that works can be used to demonstrate similarity.
  • #1
hobochu
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Homework Statement



Given two 4x4 Matrices
A = [0 -1 1 1, -1 1 0 0, 0 0 -1 1, 0 0 0 0] B = [-0.5 -0.5 -0.5 -1.5, -0.5 1.5 0.5 -0.5, 0 0 -1 1, 0 0 0 0]

I need to show that these two matrices are similar.


Homework Equations


A = SBS^-1
which simplifies to AS = SB


The Attempt at a Solution


I understand that I need to find a non-singular invertible matrix S that satisfies the equation: AS = SB, but I have spent many hours trying to find out how to find this matrix for a 4x4 matrix. In the text and in many of the online help pages, there are only examples of 2x2 matrices that have a very obvious matrix. I have not learned eigenvalues or eigenvectors yet, and do not wish to use them unless there really is no other way to show similarity.

Thanks for any responses, and I appreciate any help on this problem.
 
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  • #2
It's a matrix equation. Name the elements of the matrix S (i.e. sij), multiply the matrices in order to obtain a system of equations, and see what happens.
 
  • #3
just carring on from radou, S is not unique, if S is a solution, then so is 2S, so you just need to demonstrate any matrix that works
 

Related to Showing that two 4x4 matrices are similar

What is the definition of similarity of matrices?

The similarity of two matrices means that they have the same size and their corresponding entries have a linear relationship. This means that one matrix can be transformed into the other by using elementary row operations.

How do you determine if two matrices are similar?

To determine if two matrices are similar, you need to find their eigenvalues and eigenvectors. If the two matrices have the same eigenvalues and the corresponding eigenvectors are linearly independent, then they are similar.

What is the significance of similar matrices?

Similar matrices have the same properties and characteristics, such as determinant, trace, rank, and eigenvalues. This means that they represent the same linear transformation and can be used interchangeably in certain calculations and problems.

Can two matrices be similar if they have different dimensions?

No, two matrices must have the same dimensions in order to be similar. If they have different dimensions, they cannot represent the same linear transformation and therefore cannot be similar.

How can you prove that two matrices are similar?

To prove that two matrices are similar, you need to find a matrix P such that P-1AP = B, where A and B are the two matrices. This transformation matrix P must be invertible and can be found by using the eigenvectors and eigenvalues of the matrices.

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