A polynomial algorithm for minimizing discrete convic functions in fixed dimension

Abstract

In Chirkov et al., (2019), classes of conic and discrete conic functions were introduced. In this paper we use the term convic instead conic. The class of convic functions properly includes the classes of convex functions, strictly quasiconvex functions and the class of quasiconvex polynomials. On the other hand, the class of convic functions is properly included in the class of quasiconvex functions. The discrete convic function is a discrete analogue of the convic function. In Chirkov et al., (2019), the lower bound 3n−1log(2ρ−1) for the number of calls to the comparison oracle needed to find the minimum of the discrete convic function defined on integer points of some n-dimensional ball with radius ρ was obtained. But the problem of the existence of a polynomial (in logρ for fixed n) algorithm for minimizing such functions has remained open. In this paper, we answer positively the question of the existence of such an algorithm. Namely, we propose an algorithm for minimizing discrete convic functions that uses 2O(n2logn)logρ calls to the comparison oracle and has 2O(n2logn)poly(logρ) bit complexity.