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math.AG2019★ 11 cited
Kippenhahn's Theorem for joint numerical ranges and quantum states
Daniel Plaumann, Rainer Sinn, Stephan Weis
Kippenhahn's Theorem asserts that the numerical range of a matrix is the convex hull of a certain algebraic curve. Here, we show that the joint numerical range of finitely many Her…
math.AG2019★ 1 cited
Sums of Squares and Quadratic Persistence on Real Projective Varieties
Grigoriy Blekherman, Rainer Sinn, Gregory G. Smith +1
We bound the Pythagoras number of a real projective subvariety: the smallest positive integer such that every sum of squares of linear forms in its homogeneous coordinate ring…