Why is Cramer's rule for determinants not 'symmetric'?

Click For Summary

Discussion Overview

The discussion revolves around the application of Cramer's rule in solving non-homogeneous linear equations and the symmetry of determinants when considering row and column operations. Participants explore whether it is valid to replace rows in the context of Cramer's rule, comparing it to the use of elementary transformations for obtaining inverses.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant asserts that Cramer's rule is valid only when replacing columns and questions the feasibility of replacing rows in the process.
  • Another participant argues that swapping rows and columns does not change a determinant, implying that row replacement should be possible.
  • A third participant clarifies that in Cramer's rule, the vector is treated as a column in the matrix equation, suggesting that replacing it with a row would alter the determinant and the data being represented.
  • A fourth participant assumes that the original question may refer to taking the transpose of the matrix, indicating a possible misunderstanding of the question's intent.

Areas of Agreement / Disagreement

Participants express differing views on the validity of replacing rows in Cramer's rule, with no consensus reached on the implications of such an operation.

Contextual Notes

There are assumptions about the definitions of row and column operations and their effects on determinants that remain unresolved. The discussion does not clarify the implications of transposing matrices in this context.

Jinius
Messages
2
Reaction score
0
we can solve non-homogeneous equations in matrix form using Cramer's rule. This rule is valid only if we are replacing the columns. Why can't we replace the rows and carry on the same? For eg we can use elementary transformations for obtaining inverses either via rows or via columns.
But we can't find solutions to non homogeneous linear equations by replacing rows. Could someone please explain this? I am in a need
 
Physics news on Phys.org
You can! Who told you you can't? Swapping rows and columns will not change a determinant.
 
HallsofIvy said:
You can! Who told you you can't? Swapping rows and columns will not change a determinant.

Au=v

Yes, but in Cramer's rule you plug v as a column in A, so you swap certain data. If you plug v as a row in A, you will swap another data, and the determinant will certainly change.

As to the question itself, I think that's how it is. In this order (Au=v) the columns of A are the coefficients of each variable u1,2,3,... Therefore to pull data on u1 you will have to swap the first column and not the first row.
 
I am asuming that, by "using rows rather than columns, the OP simply meant taking the transpose. Otherwise, the question just doesn't make sense.
 

Similar threads

  • · Replies 14 ·
Replies
14
Views
4K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 8 ·
Replies
8
Views
4K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 15 ·
Replies
15
Views
5K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 48 ·
2
Replies
48
Views
7K