a) Prove that Tr(AB) = Tr(BA). Hint: See proof of (9.13). c) If S is a symmetric matrix and A is an antisymmetric matrix, show that Tr(SA) = 0. Hint: Consider Tr(SA)" and prove that Tr(SA) = – Tr(SA).

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Chapter2: Second-order Linear Odes
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**Matrix Trace Properties and Cyclic Permutations**

The equation (9.13) states the cyclic property of the trace operation for matrices:

\[ \text{Tr}(ABC) = \text{Tr}(BCA) = \text{Tr}(CAB). \]

### Proof:

We can prove this cyclic property as follows:

1. Start with the trace of the product of matrices \(ABC\):
   \[
   \text{Tr}(ABC) = \sum_i (ABC)_{ii} = \sum_i \sum_j \sum_k A_{ij} B_{jk} C_{ki}
   \]

2. Rearrange to express in terms of matrix \(BCA\):
   \[
   = \sum_i \sum_j \sum_k B_{jk} C_{ki} A_{ij} = \text{Tr}(BCA)
   \]

3. Further rearrange to express in terms of matrix \(CAB\):
   \[
   = \sum_i \sum_j \sum_k C_{ki} A_{ij} B_{jk} = \text{Tr}(CAB)
   \]

### Important Note: 

The trace of the permutation \( \text{Tr}(ABC) \) is **not** generally equal to \( \text{Tr}(ACB) \). This distinction is crucial when working with non-commutative matrices.

The illustration is a clear demonstration of the cyclic nature of the trace operation for matrices, and an important reminder of its limitations regarding non-cyclic permutations.
Transcribed Image Text:**Matrix Trace Properties and Cyclic Permutations** The equation (9.13) states the cyclic property of the trace operation for matrices: \[ \text{Tr}(ABC) = \text{Tr}(BCA) = \text{Tr}(CAB). \] ### Proof: We can prove this cyclic property as follows: 1. Start with the trace of the product of matrices \(ABC\): \[ \text{Tr}(ABC) = \sum_i (ABC)_{ii} = \sum_i \sum_j \sum_k A_{ij} B_{jk} C_{ki} \] 2. Rearrange to express in terms of matrix \(BCA\): \[ = \sum_i \sum_j \sum_k B_{jk} C_{ki} A_{ij} = \text{Tr}(BCA) \] 3. Further rearrange to express in terms of matrix \(CAB\): \[ = \sum_i \sum_j \sum_k C_{ki} A_{ij} B_{jk} = \text{Tr}(CAB) \] ### Important Note: The trace of the permutation \( \text{Tr}(ABC) \) is **not** generally equal to \( \text{Tr}(ACB) \). This distinction is crucial when working with non-commutative matrices. The illustration is a clear demonstration of the cyclic nature of the trace operation for matrices, and an important reminder of its limitations regarding non-cyclic permutations.
(a) Prove that Tr(AB) = Tr(BA). *Hint:* See proof of (9.13).

(b) [Text is redacted]

(c) If S is a symmetric matrix and A is an antisymmetric matrix, show that Tr(SA) = 0. *Hint:* Consider Tr(SA)ᵀ and prove that Tr(SA) = -Tr(SA).
Transcribed Image Text:(a) Prove that Tr(AB) = Tr(BA). *Hint:* See proof of (9.13). (b) [Text is redacted] (c) If S is a symmetric matrix and A is an antisymmetric matrix, show that Tr(SA) = 0. *Hint:* Consider Tr(SA)ᵀ and prove that Tr(SA) = -Tr(SA).
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