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Question: If AandBare symmetric matrices, show that their commutator is antisymmetric [see equation 6.3].

Short Answer

Expert verified

The given matrices A andB symmetric, which means A=ATand B=BT.

Step by step solution

01

Symmetric matrix and Antisymmetric matrix.

A symmetric matrix is a square matrix that is identical to its transpose in linear algebra.

An antisymmetric matrix is a square matrix whose negative transpose equals its positive transpose.

02

For two symmetric matrices  A and B, the commutator is antisymmetric

The commutator of matrices and can be mathematically presented asA,B

Therefore,[A,B]=AB-BA, which is a commutator of and .

Now, transpose of commutator of matrices and is mathematically presented as,

[A,B]T=(AB-BA)T=(AB)T-(BA)T…….(Using transpose property)=BTAT-ATBT……(1)

Since, then matrices and are symmetric, which meansA=ATand B=BT.

Therefore, plugging in (1),

=-(AB-BA)$

=-[A,B]$

Hence, it is proven that[A,B]T=-[A,B], which means that the transpose of commutator of two matrices Aand B , which are symmetric, is equal to the negative of the commutator of matrices A and B. Therefore, if A and B are symmetric matrices, then their commutator is antisymmetric.

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