Let A and B be Hermitian matrices. Answer true or false for each of the statements that follow. In each case, explain or prove your answer. The eigenvalues of AB are all real.

djeljenike

djeljenike

Answered question

2021-03-06

Let A and B be Hermitian matrices. Answer true or false for each of the statements that follow. In each case, explain or prove your answer. The eigenvalues of AB are all real.

Answer & Explanation

oppturf

oppturf

Skilled2021-03-07Added 94 answers

Step 1
The given statement is False
Step 2
Counter Example:
Let A=[22i2i0] and B=[22i2i0]
A and B are Hermitian matrices
Now consider the product AB
AB=[22i2i0][22i2i0]=[4+4i24i04i04i2]
AB=[444i4i4]=[04i4i4]
Consider characteristic equation for the matrix AB to get eigenvalue
det(AλI)=|0λ4i4i4λ|=|λ4i4i4λ|=0
λ(4λ)(16i2)=0
4λ+λ2+16=0
λ2+4λ+16=0
λ=4±424(16)2
λ=4±16642
λ=4±48i2=2±23i
Clearly the eigenvalues are not real numbers.
Step 3
Answer:
The given statement is False.
Jeffrey Jordon

Jeffrey Jordon

Expert2022-01-24Added 2605 answers

Answer is given below (on video)

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