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Introduction to Quantum Mechanics · Problem A.8
Afterword — David J. Griffiths
Physics — Quantum Mechanics · matrices
Problem Given the following two matrices:
A = ( − 1 1 i 2 0 3 2 i − 2 i 2 ) , B = ( 2 0 − i 0 1 0 i 3 2 ) , \mathsf{A} = \begin{pmatrix} -1 & 1 & i \\ 2 & 0 & 3 \\ 2i & -2i & 2 \end{pmatrix}, \quad \mathsf{B} = \begin{pmatrix} 2 & 0 & -i \\ 0 & 1 & 0 \\ i & 3 & 2 \end{pmatrix}, A = − 1 2 2 i 1 0 − 2 i i 3 2 , B = 2 0 i 0 1 3 − i 0 2 ,
compute: (a) A + B \mathsf{A} + \mathsf{B} A + B , (b) A B \mathsf{A}\mathsf{B} AB , (c) [ A , B ] [\mathsf{A},\mathsf{B}] [ A , B ] , (d) A ~ \tilde{\mathsf{A}} A ~ , (e) A ∗ \mathsf{A}^* A ∗ , (f) A † \mathsf{A}^\dagger A † , (g) det ( B ) \det(\mathsf{B}) det ( B ) , and (h) B − 1 \mathsf{B}^{-1} B − 1 . Check that B B − 1 = 1 \mathsf{B}\mathsf{B}^{-1} = \mathbf{1} B B − 1 = 1 . Does A \mathsf{A} A have an inverse?
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