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Functional analysis

The complete Crouzeix conjecture

OpenAI research collection · 2 manuscripts · Source checked 2026-10-19

OpenAI's result summary

Resolves the complete Crouzeix conjecture: for every bounded operator A on a complex Hilbert space and every finite matrix-valued polynomial P, one has \lVert P[A]\rVert\le2\sup_{z∈ W(A)}\lVert P(z)\rVert, where W(A) is the numerical range. The constant 2 is sharp, independent of the matrix size, and valid in infinite dimensions.

Read the manuscripts

Short excerpts below come from OpenAI's abstracts. The full abstract and original PDF preserve the paper's precise scope.

MANUSCRIPT 01

A direct proof of the complete Crouzeix inequality

We give a direct proof of the sharp constant-two numerical-range inequality for matrix-valued polynomials in all finite base and coefficient dimensions. This resolves the complete Crouzeix conjecture in its matrix formulation, including matrices whose numerical ranges are points or line segments.

This PDF is listed in OpenAI's formalization catalogue. See the scope and dependencies before interpreting coverage.

MANUSCRIPT 02

The complete Crouzeix theorem: optimal similarity and a common positive boundary representation

We resolve the complete Crouzeix conjecture by proving the sharp constant-two numerical-range inequality for every bounded operator on a complex Hilbert space and every matrix-valued polynomial. No separability assumption is needed. The closure of the numerical range is a complete 2-spectral set, and the bound extends to finite…

Full source abstract

We resolve the complete Crouzeix conjecture by proving the sharp constant-two numerical-range inequality for every bounded operator on a complex Hilbert space and every matrix-valued polynomial. No separability assumption is needed. The closure of the numerical range is a complete 2-spectral set, and the bound extends to finite matrix-valued functions holomorphic near that closure. For a finite matrix and a bounded convex domain containing its numerical range with regular real-analytic Jordan boundary, the optimal similarity making its conformal disk image contractive is attained with condition number at most two. For the similar matrix, one continuous positive boundary density of mass the identity represents the evaluation of every matrix-valued function holomorphic near the closed domain.

This PDF is listed in OpenAI's formalization catalogue. See the scope and dependencies before interpreting coverage.

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