Rump's 100 Euro Conjecture for matrices

From papers

Let ARn×nA\in\mathbb{R}^{n\times n}, let e=(1,,1)TRne=(1,\dots,1)^T\in\mathbb{R}^n be the all-ones vector, and write A|A| for the entrywise absolute value of AA. Suppose that

Ae=ne.|A|e=ne.

Rump's 100 Euro Conjecture. There exists xRn{0}x\in\mathbb{R}^n\setminus\{0\} such that

Axx.|Ax|\ge |x|.

The condition means that every row of AA lies on the boundary of the 1\ell_1-ball of radius nn. The paper's abstract says that this conjecture is confirmed using a finite-dimensional reformulation of Ball's plank theorem, so its status is solved.

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Sources & referencesView supporting material

Primary source

Teng Zhang, “Plank theorems, Gaussian probabilistic estimates and Rump's 100 Euro conjecture”, arXiv:2603.07423 (2026).

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