On the complexity of symmetric polynomials

| openaire: EC/H2020/759557/EU//ALGOComThe fundamental theorem of symmetric polynomials states that for a symmetric polynomial fSym ∈ C[x1, x2, . . ., xn], there exists a unique “witness” f ∈ C[y1, y2, . . ., yn] such that fSym = f(e1, e2, . . ., en), where the ei’s are the elementary symmetric polynomials. In this paper, we study the arithmetic complexity L(f) of the witness f as a function of the arithmetic complexity L(fSym) of fSym. We show that the arithmetic complexity L(f) of f is bounded by poly(L(fSym), deg(f), n). To the best of our knowledge, prior to this work only exponential upper bounds were known for L(f). The main ingredient in our result is an algebraic analogue of Newton’s iteration on power series. As a corollary of this result, we show that if VP 6= VNP then there exist symmetric polynomial families which have super-polynomial arithmetic complexity. Furthermore, we study the complexity of testing whether a function is symmetric. For polynomials, this question is equivalent to arithmetic circuit identity testing. In contrast tothis, we show that it is hard for Boolean functions.Peer reviewe