Convex entire noncommutative functions are polynomials of degree two or less

J. William Helton, J. E. Pascoe, Ryan Tully-Doyle +1

This paper concerns matrix "convex" functions of (free) noncommuting variables, $x=(x_1,\dots ,x_g)$. Helton and McCullough showed that a polynomial in $x$ which is matrix conv…