Skew-Hermitian or Hermitian Matrix?

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Discussion Overview

The discussion revolves around the classification of a given matrix as either Hermitian or skew-Hermitian. Participants explore the properties of these types of matrices, particularly focusing on the implications of their diagonal elements and the conditions that define each category.

Discussion Character

  • Homework-related
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant states that the matrix in question is Hermitian, arguing that skew-Hermitian matrices cannot have real numbers on the diagonal due to the condition ##z^* = - z##.
  • Another participant agrees that for skew-Hermitian matrices, the diagonal elements are zero, but later corrects this by stating that the diagonal elements must be purely imaginary, not necessarily zero.
  • A third participant reiterates the point about skew-Hermitian matrices having zero diagonal elements, but acknowledges that this is true only for real-valued, skew-symmetric matrices.
  • It is noted that Hermitian matrices must have entirely real components on their diagonal, which could include zeros, while skew-Hermitian matrices have purely imaginary diagonal elements.

Areas of Agreement / Disagreement

Participants express differing views on the properties of skew-Hermitian matrices, particularly regarding the nature of their diagonal elements. There is no consensus on the classification of the matrix in question, as participants present competing interpretations of the definitions.

Contextual Notes

Some statements rely on specific definitions of Hermitian and skew-Hermitian matrices, and there are unresolved assumptions regarding the nature of the matrix being discussed.

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Homework Statement


upload_2018-1-30_17-7-35-png.png


Homework Equations


For Hermition: A = transpose of conjugate of A
For Skew Hermition A = minus of transpose of conjugate of A

The Attempt at a Solution


I think this answer is C. As Tranpose of conjugate of matrix is this matrix.
Book answer is D.
Am I wrong or is book wrong?
 

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It is obviously Hermitian. It cannot be skew-hermitian. Skew-hermitian matrices cannot have real numbers on the diagonal as the diagonal elements need to satisfy ##z^* = - z##.
 
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Yeah. For skew hermitian, the diagonal elements are zero.
 
jaus tail said:
Yeah. For skew hermitian, the diagonal elements are zero.
This is not correct. The diagonal elements would be purely imaginary but not necessarily zero.
 
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jaus tail said:
Yeah. For skew hermitian, the diagonal elements are zero.

This holds if you are talking about real valued, skew symmetric matrices. But you aren't.
- - - -
the flip side is a Hermitian matrix must have entirely real components on its diagonal.

So Hermitian has purely real diagonal (possibly all zeros). Skew Hermitian has purely imaginary diagonal (possibly all zeros).

This should give you a hint at how these two matrices 'fit together'.
 
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