Linear Algebra (Meaning of Rank)

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SUMMARY

The rank of an n x n matrix A is definitively equal to the number of linearly independent row vectors in A. This statement holds true specifically for square matrices, as the equality of row rank and column rank applies only when the number of rows equals the number of columns. In cases where the matrix is not square (n x m with n ≠ m), the row rank and column rank may differ, which is crucial for understanding linear independence in those scenarios.

PREREQUISITES
  • Understanding of matrix dimensions (n x n, n x m)
  • Knowledge of linear independence in vector spaces
  • Familiarity with the concepts of row rank and column rank
  • Basic understanding of linear algebra terminology
NEXT STEPS
  • Study the implications of row and column rank in non-square matrices
  • Learn about the Rank-Nullity Theorem in linear algebra
  • Explore applications of matrix rank in solving linear equations
  • Investigate methods for determining the rank of a matrix, such as Gaussian elimination
USEFUL FOR

Students of linear algebra, educators teaching matrix theory, and anyone seeking to deepen their understanding of matrix properties and their applications in various mathematical contexts.

DanielFaraday
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Homework Statement



True or False:
If A is an n x n matrix, then the rank of A equals the number of linearly independent row vectors in A.

Homework Equations



None


The Attempt at a Solution



Okay, I know this is a ridiculously easy question, but I'm wondering if there is a catch to it. My inclination is to say this is true. But wouldn't this be true for ANY matrix? Why does the question limit it to an n x n matrix? Are they just being tricky?
 
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DanielFaraday said:

Homework Statement



True or False:
If A is an n x n matrix, then the rank of A equals the number of linearly independent row vectors in A.

Homework Equations



None


The Attempt at a Solution



Okay, I know this is a ridiculously easy question, but I'm wondering if there is a catch to it. My inclination is to say this is true. But wouldn't this be true for ANY matrix? Why does the question limit it to an n x n matrix? Are they just being tricky?

Well, if it were n x m with n not equal to m, then the row rank and column rank would not generally be the same, right?

Also, if you have more rows than columns, what can you say about the linear independence of the rows...?

http://en.wikipedia.org/wiki/Rank_(linear_algebra )

.
 
Last edited by a moderator:
berkeman said:
Well, if it were n x m with n not equal to m, then the row rank and column rank would not generally be the same, right?

Also, if you have more rows than columns, what can you say about the linear independence of the rows...?

http://en.wikipedia.org/wiki/Rank_(linear_algebra )

.

Thanks for your reply. In the wikipedia article that you cited (which I had read before posting this question) it says in the third sentence: "Since the column rank and the row rank are always equal, they are simply called the rank of A". I believe this statement is correct, which disagrees with your first point. Am I missing something?
 
Last edited by a moderator:
DanielFaraday said:
Thanks for your reply. In the wikipedia article that you cited (which I had read before posting this question) it says in the third sentence: "Since the column rank and the row rank are always equal, they are simply called the rank of A". I believe this statement is correct, which disagrees with your first point. Am I missing something?

No, that sentence was my point. if n=m, then you use the term "rank" instead of differentiating between rows and columns. I think your original answer is correct, just that it cannot be extended always to cases where n is not equal to m. Hope I'm not just adding confusion here...
 
Okay, that makes perfect sense. Thank you!
 

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