Author

# Prakod Ngamlamai

Bio: Prakod Ngamlamai is an academic researcher. The author has contributed to research in topics: Mathematics. The author has co-authored 2 publications.

Topics: Mathematics

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03 Oct 2022

TL;DR: For the generalized dihedral group D = Z 2 (cid:110) G, the authors showed that there are more MSTD sets than MDTS sets when 6 ≤ m ≤ c j √ n for c j = 1 . 3229 / √ 111 + 5 j , where j is the number of elements in G with order at most 2.

Abstract: . Given a group G , we say that a set A ⊆ G has more sums than diﬀerences (MSTD) if | A + A | > | A − A | , has more diﬀerences than sums (MDTS) if | A + A | < | A − A | , or is sum-diﬀerence balanced if | A + A | = | A − A | . A problem of recent interest has been to understand the frequencies of these type of subsets. The seventh author and Vissuet studied the problem for arbitrary ﬁnite groups G and proved that almost all subsets A ⊆ G are sum-diﬀerence balanced as | G | → ∞ . For the dihedral group D 2 n , they conjectured that of the remaining sets, most are MSTD, i.e., there are more MSTD sets than MDTS sets. Some progress on this conjecture was made by Haviland et al. in 2020, when they introduced the idea of partitioning the subsets by size: if, for each m , there are more MSTD subsets of D 2 n of size m than MDTS subsets of size m , then the conjecture follows. We extend the conjecture to generalized dihedral groups D = Z 2 (cid:110) G , where G is an abelian group of size n and the nonidentity element of Z 2 acts by inversion. We make further progress on the conjecture by considering subsets with a ﬁxed number of rotations and reﬂections. By bounding the expected number of overlapping sums, we show that the collection S D,m of subsets of the generalized dihedral group D of size m has more MSTD sets than MDTS sets when 6 ≤ m ≤ c j √ n for c j = 1 . 3229 / √ 111 + 5 j , where j is the number of elements in G with order at most 2. We also analyze the expectation for | A + A | and | A − A | for A ⊆ D 2 n , proving an explicit formula for | A − A | when n is prime.

20 Oct 2022

TL;DR: In this paper , the authors studied the probabilistic aspects of random Zeckendorf games and showed that for any input N , the range of possible game lengths constitutes an interval of natural numbers: every game length between the shortest and longest game lengths can be achieved.

Abstract: . Zeckendorf proved that any positive integer has a unique decomposition as a sum of non-consecutive Fibonacci numbers, indexed by F 1 = 1 , F 2 = 2 , F n +1 = F n + F n − 1 . Motivated by this result, Baird, Epstein, Flint, and Miller [3] deﬁned the two-player Zeckendorf game, where two players take turns acting on a multiset of Fibonacci numbers that always sums to N . The game terminates when no possible moves remain, and the ﬁnal player to perform a move wins. Notably, [3] studied the setting of random games: the game proceeds by choosing an available move uniformly at random, and they conjecture that as the input N → ∞ , the distribution of random game lengths converges to a Gaussian. We prove that certain sums of move counts is constant, and ﬁnd a lower bound on the number of shortest games on input N involving the Catalan numbers. The works [3] and Cuzensa et al. [5] determined how to achieve a shortest and longest possible Zeckendorf game on a given input N , respectively: we establish that for any input N , the range of possible game lengths constitutes an interval of natural numbers: every game length between the shortest and longest game lengths can be achieved. We further the study of probabilistic aspects of random Zeckendorf games. We study two probability measures on the space of all Zeckendorf games on input N : the uniform measure, and the measure induced by choosing moves uniformly at random at any given position. Under both measures that in the limit N → ∞ , both players win with probability 1 / 2. We also ﬁnd natural partitions of the collection of all Zeckendorf games of a ﬁxed input N , on which we observe weak convergence to a Gaussian in the limit N → ∞ . We conclude the work with many open problems.