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math.FA2026
The joint numerical range of three hermitian matrices
Piotr Pikul, Ilya Spitkovsky, Konrad SzymaÅski +2
We analyze the joint numerical range of three hermitian matrices of order four. In the generic case, this three-dimensional convex set has a smooth boundary. We analyze non-gen…
math.FA2025
Matrix systems, algebras, and open maps
Stephan Weis
Every state on the algebra of complex nxn matrices restricts to a state on any matrix system. Whereas the restriction to a matrix system is generally not open, we prove that…