A Norm Compression Inequality for Block Partitioned Positive Semidefinite Matrices

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dc.creatorAudenaert, Koenraad M. R.
dc.date2005-05-31
dc.date.accessioned2026-07-07T08:27:49Z
dc.date.available2026-07-07T08:27:49Z
dc.descriptionLet $A$ be a positive semidefinite matrix, block partitioned as $$ A=\twomat{B}{C}{C^*}{D}, $$ where $B$ and $D$ are square blocks. We prove the following inequalities for the Schatten $q$-norm $||.||_q$, which are sharp when the blocks are of size at least $2\times2$: $$ ||A||_q^q \le (2^q-2) ||C||_q^q + ||B||_q^q+||D||_q^q, \quad 1\le q\le 2, $$ and $$ ||A||_q^q \ge (2^q-2) ||C||_q^q + ||B||_q^q+||D||_q^q, \quad 2\le q. $$ These bounds can be extended to symmetric partitionings into larger numbers of blocks, at the expense of no longer being sharp: $$ ||A||_q^q \le \sum_{i} ||A_{ii}||_q^q + (2^q-2) \sum_{i<j} ||A_{ij}||_q^q, \quad 1\le q\le 2, $$ and $$ ||A||_q^q \ge \sum_{i} ||A_{ii}||_q^q + (2^q-2) \sum_{i<j} ||A_{ij}||_q^q, \quad 2\le q. $$
dc.description24 pages
dc.identifierhttps://arxiv.org/abs/math/0505680
dc.identifierhttp://arxiv.org/abs/math/0505680
dc.identifierLin. Alg. Appl. 413, 155-176 (2006).
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/137404
dc.subjectFunctional Analysis
dc.subjectMathematical Physics
dc.subject15A60
dc.titleA Norm Compression Inequality for Block Partitioned Positive Semidefinite Matrices
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