The aim of the article was to analyze the impact of outliers on the accuracy of intermittent demand forecasting. The hypothesis was verified that eliminating the influence of outliers leads to more accurate forecasts. A data set containing monthly sales time series of over 12 000 products was analyzed. Three outliers rejection strategies were analyzed (replacing outliers, replacing extreme values, isolation forest). Intermittent demand forecasts were determined using the Croston, SBA, TSB and SES methods, with optimization of smoothing constants and initial values. The accuracy of the forecasts was assessed from the point of view of the inventories value and the value of lost sales (lost demand). The conducted research shows that eliminating the influence of outliers significantly reduces the inventory level value, with only a slight increase in the value of lost sales. Eliminating the influence of outliers therefore provides an opportunity to improve the financial results of enterprises selling slow – moving products through a significant reduction in inventory levels.

A long-standing conjecture of Zsolt Tuza asserts that the triangle covering number $\tau(G)$ is at most twice the triangle packing number $\nu(G)$, where the triangle packing number $\nu(G)$ is the maximum size of a set of edge-disjoint triangles in $G$ and the triangle covering number $\tau(G)$ is the minimal size of a set of edges intersecting all triangles. In this paper, we prove that Tuza's conjecture holds in the Erdös--Rényi random graph $G(n,m)$ for all ranges of $m$, closing the “gap” in what was previously known. (Recently, this result was also independently proved by Jeff Kahn and Jinyoung Park.) We employ a random greedy process called the online triangle packing process to produce a triangle packing in $G(n,m)$ and analyze this process by using the differential equations method.

The game of plates and olives was originally formulated by Nicolaescu and encodes the evolution of the topology of the sublevel sets of Morse functions. We consider a random variant of this game. The process starts with an empty table. There are four different types of moves: (1) add a new plate to the table, (2) combine two plates and their olives onto one plate, removing the second plate from the table, (3) add an olive to a plate, and (4) remove an olive from a plate. We show that with high probability the number of olives is linear as the total number of moves goes to infinity. Furthermore, we prove that the number of olives is concentrated around its expectation.

The size-Ramsey number ${R}{F}$ of a graph $F$ is the smallest integer $m$ such that there exists a graph $G$ on $m$ edges with the property that any coloring of the edges of $G$ with two colors yields a monochromatic copy of $F$. In this paper, first we focus on the size-Ramsey number of a path $P_n$ on $n$ vertices. In particular, we show that $5n/2-15/2 \le {R}(){P_n} \le 74n$ for $n$ sufficiently large. (The upper bound uses expansion properties of random $d$-regular graphs.) This improves the previous lower bound, ${R}{P_n} \ge (1+\sqrt{2})n-O(1)$, due to Bollobás, and the upper bound, ${R}(){P_n} \le 91n$, due to Letzter. Next we study long monochromatic paths in an edge-colored random graph $\mathcal{G}(n,p)$ with $pn \to \infty$. Let $\alpha > 0$ be an arbitrarily small constant. Recently, Letzter showed that asymptotically almost surely (a.a.s.) any $2$-edge coloring of $\mathcal{G}(n,p)$ yields a monochromatic path of length $(2/3-\alpha)n$, which is optimal. Extending this result, we show that a.a.s. any $3$-edge coloring of $\mathcal{G}(n,p)$ yields a monochromatic path of length $(1/2-\alpha)n$, which is also optimal. We also consider a related problem and show that for any $r \ge 2$, a.a.s. any $r$-edge coloring of $\mathcal{G}(n,p)$ yields a monochromatic connected subgraph on $(1/(r-1)-\alpha)n$ vertices, which is also tight.

Benjamini, Shinkar, and Tsur stated the following conjecture on the acquaintance time: asymptotically almost surely ${\mathcal A \mathcal C}(G) \le p^{-1} \log^{O(1)} n$ for a random graph $G \in G(n,p)$, provided that $G$ is connected. Recently, Kinnersley, Mitsche, and Prałat made a major step toward this conjecture by showing that asymptotically almost surely ${\mathcal A \mathcal C}(G) = O(\log n / p)$, provided that $G$ has a Hamiltonian cycle. In this paper, we finish the task by showing that the conjecture holds in the strongest possible sense, that is, it holds right at the time the random graph process creates a connected graph. Moreover, we generalize and investigate the problem for random hypergraphs.

An edge colored graph $G$ is rainbow edge connected if any two vertices are connected by a path whose edges have distinct colors. The rainbow connection of a connected graph $G$, denoted by $rc(G)$, is the smallest number of colors that are needed in order to make $G$ rainbow connected. In this work we study the rainbow connection of the random $r$-regular graph $G=G(n,r)$ of order $n$, where $r\ge 4$ is a constant. We prove that with probability tending to one as $n$ goes to infinity the rainbow connection of $G$ satisfies $rc(G)=O(\log n)$, which is best possible up to a hidden constant.

We study a problem motivated by a question related to quantum error-correcting codes. Combinatorially, it involves the graph parameter $f(G)=\min\{|A|+|\{x\in V\setminus A:d_A(x)$ is $\text{odd}\}|:A\neq\emptyset\}$, where V is the vertex set of G and $d_A(x)$ is the number of neighbors of x in A. We give asymptotically tight estimates of f for the random graph $G_{n,p}$ when p is constant. Also, if $f(n)=\max\{f(G):\,|V(G)|=n\}$, then we show that $f(n)\leq(0.382+o(1))n$.