Border Rank Nonadditivity for Higher Order Tensors

M. Christandl, F. Gesmundo, M. Michałek, J. Zuiddam

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Abstract

Whereas matrix rank is additive under direct sum, in 1981 Schönhage showed that one of its generalizations to the tensor setting, tensor border rank, can be strictly subadditive for tensors of order three. Whether border rank is additive for higher order tensors has remained open. In this work, we settle this problem by providing analogues of Schönhage's construction for tensors of order four and higher. Schönhage's work was motivated by the study of the computational complexity of matrix multiplication; we discuss implications of our results for the asymptotic rank of higher order generalizations of the matrix multiplication tensor.
Original languageEnglish
JournalSIAM Journal on Matrix Analysis and Applications
Volume42
Issue number2
Pages (from-to)503-527
ISSN0895-4798
DOIs
Publication statusPublished - 2021

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