Elementary Linear Algebra - Similar Matrices and Rank

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Homework Help Overview

The discussion revolves around the properties of similar matrices, specifically focusing on the relationship between their ranks. The original poster presents a scenario where two matrices, A and B, are similar, and seeks to understand why they must have the same rank.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to connect the rank of matrix A to the rank of the expression P^-1AP, questioning the underlying intuition. Some participants inquire about the definition of rank and its implications in the context of linear transformations, while others explore the idea of bases and their relationship to the rank of similar matrices.

Discussion Status

The discussion is active, with participants providing insights into the definition of rank and its connection to linear transformations. There is an exploration of whether the relationship can be understood without referencing transformations, indicating a productive line of questioning.

Contextual Notes

Participants are navigating the definitions and properties of rank and similarity, with some expressing uncertainty about the concepts involved. There is a focus on understanding the implications of similarity in the context of linear algebra.

Rockoz
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Homework Statement


Suppose matrices A and B are similar. Explain why they have the same rank.



Homework Equations





The Attempt at a Solution


So if A and B are similar, then there is some invertible matrix P such that B = P^-1AP. I have been trying to find some way to relate rank(A) to rank(P^-1AP) but I can't figure it out. I feel like maybe I'm missing some intuition about this. This comes at the end of a section about linear transformations.

Thank you to anyone who can help.
 
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What is the definition of "rank"?
 
"The dimension of the row (or column) space of a matrix is called the rank of A and is denoted by rank(A)."

Thinking about this I recall that the rank of a linear transformation is equal to the rank of the matrix for T (where T is defined by T(x) = Ax). So if A and B both represent the same linear transformation but with respect to different bases, then they will have the same rank. This relationship is described by them being similar. P and P^-1 are the transition matrices between the bases.

Is my thinking headed in the right direction? I still feel unclear about this. Is there a way to discuss this without reference to transformations and just from the definition of being similar?

Thank you for your time.
 
The rank of A is the dimension of the image of A. So take a basis of the image of A. Can you maje this into a basis of the image of PAP^{-1}??
 

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