.3.5. For n×n matrices A and B, explain why each of the following in- equalities is valid. (a) trace (B)² ≤n [trace (B*B)]. (b) trace (B²) ≤ trace (BTB) for real matrices. (c) trace (ATB) ≤ trace (ATA) + trace (BTB) 2 for real matrices.

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Chapter2: Second-order Linear Odes
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### 5.3.5. Matrix Inequalities

For \( n \times n \) matrices **A** and **B**, explain why each of the following inequalities is valid.

#### (a)
\[ | \text{trace}(\mathbf{B}) |^2 \leq n [ \text{trace}(\mathbf{B}^* \mathbf{B}) ]. \]

#### (b)
\[ \text{trace}(\mathbf{B}^2) \leq \text{trace}(\mathbf{B}^T \mathbf{B}) \text{ for real matrices}. \]

#### (c)
\[ \text{trace}(\mathbf{A}^T \mathbf{B}) \leq \frac{\text{trace}(\mathbf{A}^T \mathbf{A}) + \text{trace}(\mathbf{B}^T \mathbf{B})}{2} \text{ for real matrices}. \]

### Explanation
These inequalities are mathematical expressions involving the trace function, which is the sum of the elements on the main diagonal of a matrix. Each inequality has specific conditions or operations, such as transposition (denoted as \( \mathbf{B}^T \)) and conjugate transpose (denoted as \( \mathbf{B}^* \)).

Understanding these inequalities helps in various mathematical and physical applications, particularly in matrix analysis and quantum mechanics.
Transcribed Image Text:### 5.3.5. Matrix Inequalities For \( n \times n \) matrices **A** and **B**, explain why each of the following inequalities is valid. #### (a) \[ | \text{trace}(\mathbf{B}) |^2 \leq n [ \text{trace}(\mathbf{B}^* \mathbf{B}) ]. \] #### (b) \[ \text{trace}(\mathbf{B}^2) \leq \text{trace}(\mathbf{B}^T \mathbf{B}) \text{ for real matrices}. \] #### (c) \[ \text{trace}(\mathbf{A}^T \mathbf{B}) \leq \frac{\text{trace}(\mathbf{A}^T \mathbf{A}) + \text{trace}(\mathbf{B}^T \mathbf{B})}{2} \text{ for real matrices}. \] ### Explanation These inequalities are mathematical expressions involving the trace function, which is the sum of the elements on the main diagonal of a matrix. Each inequality has specific conditions or operations, such as transposition (denoted as \( \mathbf{B}^T \)) and conjugate transpose (denoted as \( \mathbf{B}^* \)). Understanding these inequalities helps in various mathematical and physical applications, particularly in matrix analysis and quantum mechanics.
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