Inverse problems for certain subsequence sums in integers

Abstract

Let $A$ be a nonempty finite set of $k$ integers. Given a subset $B$ of $A$, the sum of all elements of $B$, denoted by $s(B)$, is called the subset sum of $B$. For a nonnegative integer $\alpha$ ($\leq k$), let \[\Sigma_{\alpha} (A):=\{s(B): B \subset A, |B|\geq \alpha\}.\] Now, let $\mathcal{A}=(\underbrace{a_{1},\ldots,a_{1}}_{r_{1}~\text{copies}}, \underbrace{a_{2},\ldots,a_{2}}_{r_{2}~\text{copies}},\ldots, \underbrace{a_{k},\ldots,a_{k}}_{r_{k}~\text{copies}})$ be a finite sequence of integers with $k$ distinct terms, where $r_{i}\geq 1$ for $i=1,2,\ldots,k$. Given a subsequence $\mathcal{B}$ of $\mathcal{A}$, the sum of all terms of $\mathcal{B}$, denoted by $s(\mathcal{B})$, is called the subsequence sum of $\mathcal{B}$. For $0\leq \alpha \leq \sum_{i=1}^{k} r_{i}$, let \[\Sigma_{\alpha} (\bar{r},\mathcal{A}):=\left\{s(\mathcal{B}): \mathcal{B}~\text{is a subsequence of}~\mathcal{A}~\text{of length} \geq \alpha \right\},\] where $\bar{r}=(r_{1},r_{2},\ldots,r_{k})$. Very recently, Balandraud obtained the minimum cardinality of $\Sigma_{\alpha} (A)$ in finite fields. Motivated by Baladraud's work, we find the minimum cardinality of $\Sigma_{\alpha}(A)$ in the group of integers. We also determine the structure of the finite set $A$ of integers for which $|\Sigma_{\alpha} (A)|$ is minimal. Furthermore, we generalize these results of subset sums to the subsequence sums $\Sigma_{\alpha} (\bar{r},\mathcal{A})$. As special cases of our results we obtain some already known results for the usual subset and subsequence sums.