Determinant Identity for A-B and B A Matrices

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    Determinant Identity
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Discussion Overview

The discussion revolves around the determinant of a specific block matrix formed by two nxn square matrices, A and B. Participants explore potential identities or properties related to this determinant, considering various conditions and limitations.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about an identity for the determinant of the block matrix composed of A and B.
  • Another participant suggests a resource that may provide relevant information regarding block matrices.
  • A third participant points to Wikipedia as a source for determinant properties of block matrices.
  • One participant expresses skepticism about the applicability of existing formulas due to the lack of commutativity and invertibility of A and B in their specific case.
  • This same participant asserts that the determinant is nonzero and likely positive, indicating a need to demonstrate this claim.
  • A later reply proposes investigating patterns in determinants of smaller block matrices (2x2, 4x4, 9x9) as a potential approach.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the applicability of existing determinant formulas, and multiple competing views regarding the properties of A and B remain unresolved.

Contextual Notes

Participants note limitations regarding assumptions about the commutativity and invertibility of matrices A and B, which affect the applicability of standard determinant identities.

quasar987
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Hello matrices masters,

If A and B are nxn square matrices, is there an identity for the determinant of the block matrix

A -B
B A

?

Lots of thanks and praises.
 
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Would http://www.mth.kcl.ac.uk/~jrs/gazette/blocks.pdf be able to help you out?
 
Last edited by a moderator:
Unfortunately, in the particular case I'm interested in, I don't see a reason to believe that A and B commute, nor that A or B is invertible. So none of the formulae on wiki are applicable.

I know for a fact that the determinant of that matrix is nonzero, and it is probably positive, which I am trying to show.
 
Did you try finding a pattern between the 2x2, 4x4, 9x9?
 

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