The Determinant of a Matrix of Matrices

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Discussion Overview

The discussion revolves around finding the determinant of a specific block matrix composed of an n-by-n matrix L and an m-by-n matrix A. Participants explore various approaches and reasoning related to the determinant's calculation, including potential simplifications and counterexamples.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents the matrix structure and asks how to find its determinant.
  • Another participant suggests that the determinant could be expressed as det(-AA').
  • A follow-up request for elaboration on the previous suggestion indicates a need for clarification on the reasoning behind it.
  • Another participant claims that terms containing elements of L will contain zeroes, implying that the determinant's calculation may simplify under certain conditions.
  • A subsequent question challenges the reasoning behind the assertion that terms with elements of L will contain zeroes.
  • A participant disputes the earlier suggestion of det(-AA') being correct, providing a counterexample with specific matrices L and A, indicating that the determinant calculation involves non-zero contributions from L.
  • This participant concludes that there may not be a "simple" formula for the determinant of the given matrix structure.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the determinant expression det(-AA') and whether terms involving L contribute to the determinant. The discussion remains unresolved, with multiple competing perspectives on the calculation and its implications.

Contextual Notes

Limitations include the dependence on the specific forms of matrices L and A, as well as unresolved mathematical steps in the determinant calculation. The discussion does not reach a consensus on a definitive formula or approach.

EngWiPy
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Hi,

Suppose we have the following matrix:

[tex]\begin{center}\begin{pmatrix}\mathbf{L}&\mathbf{A}^T\\\mathbf{A}&\mathbf{0}\end{pmatrix}\end{center}[/tex]

where L is n-by-n matrix, A is m-by-n matrix. How to find the determinant of this square matrix?

Thanks in advance
 
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det(-AA')
 
Some Pig said:
det(-AA')

Thank you for replying, but can you elaborate more, please?
 
Terms containing elements of L will contains zeroes,
so terms only containing elements of A and A'.
The negative sign indicates orders of the elements.
 
Some Pig said:
Terms containing elements of L will contains zeroes...

Why is that?
 
Some Pig said:
det(-AA')

This is wrong.

Counterexample:

[tex]L = \begin{pmatrix} 2 & 0 \cr 0 & 2 \end{pmatrix} \quad <br /> A = \begin{pmatrix} 1 \cr 0\end{pmatrix}[/tex]

Working out the 3x3 determinant shows the mistake in the "proof" that it was right. The only non-zero product in the determinant does contain an element of L.

I don't think there is any "simple" formula for this.
 

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