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Consider the polynomial of degree $4$ in variable $r$ $$ r^4 + (x^2 + y^2)\ r^2 - 2 x y\ r + x^2 y^2 $$ The discriminant of this polynomial in $r$ is the following expression (obtained using ...

I have an engineering problem that may be solved using semidefinite programming. I would like to know whether a given set is convex. Let $m \in \mathbb{R}^+$ be a positive real scalar, $l \in \mathbb{...