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Hadamard's inequality (Theorem)

Let $A=(a_{ij})$ with $1\leq i,j\leq n\in\mathbb{N}$ be a square matrix with complex coefficients. Then the following inequality holds: $$|\det(A)|\leq \prod_{i=1}^n\left(\sum_{j=1}^n|a_{ij}|^2\right)^\frac{1}{2}.$$ Moreover, if $A$ is Hermitian and positive semidefinite, the following inequality holds: $$\det(A)\leq \prod_{i=1}^n a_{ii},$$ with equality if and only if $A$ is a diagonal matrix.




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proof of Hadamard's inequality (Proof) by Andrea Ambrosio
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Cross-references: diagonal matrix, equality, positive semidefinite, Hermitian, inequality, coefficients, complex, square matrix
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This is version 6 of Hadamard's inequality, born on 2004-08-08, modified 2006-08-21.
Object id is 6084, canonical name is HadamardsInequality.
Accessed 7438 times total.

Classification:
AMS MSC15A45 (Linear and multilinear algebra; matrix theory :: Miscellaneous inequalities involving matrices)

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