The alternative conjecture on the spectral norm of Gaussian random matrices

Let XX be the d×dd\times d symmetric random matrix with entries Xij=bijgijX_{ij}=b_{ij}g_{ij}, where {gij:ij}\{g_{ij}:i\ge j\} are independent standard Gaussian random variables and {bij:ij}\{b_{ij}:i\ge j\} are given nonnegative scalars. For a symmetric matrix, X2X^2 denotes its square, and \|\cdot\| denotes the operator norm. Alternative spectral-norm conjecture. The expected spectral norm satisfies

EXEX21/2+EmaxijXij.\mathbf{E}\|X\|\asymp\|\mathbf{E}X^2\|^{1/2}+\mathbf{E}\max_{ij}|X_{ij}|.

This formulation is motivated by a dimension-dependent upper bound whose first term equals EX21/2\|\mathbf{E}X^2\|^{1/2} and whose second term controls the expected largest entry. The source presents it as an alternative to Latała's conjecture and does not provide a resolution.

Sources & referencesView supporting material

Primary source

Ramon van Handel, “On the spectral norm of Gaussian random matrices”, arXiv:1502.05003 (2016).

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