# The generalized k-resultant modulus set problem in finite fields

Research paper by **David Covert, Doowon Koh, Youngjin Pi**

Indexed on: **01 Mar '17**Published on: **01 Mar '17**Published in: **arXiv - Mathematics - Combinatorics**

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#### Abstract

Let $\mathbb F_q^d$ be the $d$-dimensional vector space over the finite field
$\mathbb F_q$ with $q$ elements. Given $k$ sets $E_j\subset \mathbb F_q^d$ for
$j=1,2,\ldots, k$, the generalized $k$-resultant modulus set, denoted by
$\Delta_k(E_1,E_2, \ldots, E_k)$, is defined by \[ \Delta_k(E_1,E_2, \ldots,
E_k)=\left\{\|x^1+x^2+\cdots+x^k\|\in \mathbb F_q:x^j\in E_j,\, j=1,2,\ldots,
k\right\},\] where $\|y\|=y_1^2+ \cdots + y_d^2$ for $y=(y_1, \ldots, y_d)\in
\mathbb F_q^d.$ We prove that if $\prod\limits_{j=1}^3 |E_j| \ge C
q^{3\left(\frac{d+1}{2} -\frac{1}{6d+2}\right)}$ for $d=4,6$ with a
sufficiently large constant $C>0$, then $|\Delta_3(E_1,E_2,E_3)|\ge cq$ for
some constant $0<c\le 1,$ and if $\prod\limits_{j=1}^4 |E_j| \ge C
q^{4\left(\frac{d+1}{2} -\frac{1}{6d+2}\right)}$ for even $d\ge 8,$ then
$|\Delta_4(E_1,E_2,E_3, E_4)|\ge cq.$ We also show that if
$\prod\limits_{j=1}^3 |E_j| \ge C q^{3\left(\frac{d+1}{2}
-\frac{1}{9d-18}\right)}$ for even $d\ge 8,$ then $|\Delta_3(E_1,E_2,E_3)|\ge
cq.$ This work both generalizes and improves previous work by the authors.