Let \( A, B \) are \( n \times n \) Hermitian matrices and \( p, q \in [1, \infty] \) with \( \frac{1}{p} + \frac{1}{q} = 1 \). Prove that

\[

| Tr (AB) | \leq \| A \|_{S^p} \| B \|_{S^q}.

\]

(Here, \(\| A \|_{S^p} \) is the \(p\)-Schatten norm of \( A \), defined by

\[

\| A \|_{S^p} = \left( \sum_{i=1}^n |\lambda_i|^p \right)^{1/p},

\]

where \( \lambda_1, \lambda_2, \dots, \lambda_n \) are the eigenvalues of \( A \).)

The best solution was submitted by Park, Sunghyuk (박성혁, 수리과학과 2014학번). Congratulations!

Here is his solution of problem 2015-24.

Alternative solutions were submitted by 신준형 (2015학번, +3), 이정환 (2015학번, +3), 이종원 (수리과학과 2014학번, +3), 장기정 (수리과학과 2014학번, +3), 김동률 (2015학번, +2), 최인혁 (2015학번, +2).

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