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1

Weak signed Roman k-domination in digraphs

Volkmann Lutz

Opuscula Mathematica

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2024

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Vol. 44, no. 2

285--296

EN

Let k ≥ 1 be an integer, and let D be a finite and simple digraph with vertex set V (D). A weak signed Roman k-dominating function (WSRkDF) on a digraph D is a function f : V (D) → {−1, 1, 2} satisfying the condition that ∑x∈N−[v] f(x) ≥ k for each v ∈ V (D), where N−[v] consists of v and all vertices of D from which arcs go into v. The weight of a WSRkDF f is w(f) = ∑v∈V (D) f(v). The weak signed Roman k-domination number [formula] is the minimum weight of a WSRkDF on D. In this paper we initiate the study of the weak signed Roman k-domination number of digraphs, and we present different bounds on [formula]. In addition, we determine the weak signed Roman k-domination number of some classes of digraphs. Some of our results are extensions of well-known properties of the weak signed Roman domination number [formula] and the signed Roman k-domination number [formula].

2

The Complete Set of Distinguishable Diagnostic States for a Centrifugal Pump System

Szczepański Paweł, Kijak Robert

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2023

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Vol. 14, Nr 3 (53)

95--118

EN

In this article, the concept of determination of a complete set of distinguishable diagnostic states has been utilised, which has been well known since the 1980’s and, in essence, could refer to any item with any application and any structural features. The only condition set for this item, is its ability to be described by a structure consisting of single exit-point elements. As a consequence, it can become possible to assess, amongst other things, its layers, strong cohesions, transitive and antitransitive closures. Typical tools of such assessment are matrices: transition and reachability. The reason that a centrifugal pump has been selected is not only its importance and common use, but also specifics of interaction of its elements. It is possible to identify for them: independence, dependence, and interdependence. For particular distinguishable diagnostic states, the probabilities of its occurrence have been determined. These probabilities have become a starting point to estimate structure entropy and intensity of transition from the health to any particular failure state. Results of such estimation have been depicted by relevant graphs. A reference has been made to the Bayesian methods and the inseparable ‘serial reliability structure’, to identify their flaws that result particularly from simplifications leading to false and ambiguous diagnoses. The probabilities of health for particular elements have been differentiated by the selection of adequate Weibull indices.

PL

W artykule posłużono się, znaną od lat osiemdziesiątych ubiegłego wieku, koncepcją wyznaczania pełnego zbioru rozróżnialnych stanów diagnostycznych, która w istocie rzeczy może odnieść się do dowolnego obiektu o dowolnym przeznaczeniu i dowolnych cechach konstrukcyjnych. Jedyny warunek jaki stawia się przed obiektem to możliwość jego opisu strukturą połączeń elementów jednowyjściowych. Konsekwencją stanie się wtedy możliwość poznania m.in. jego: warstw, silnych spójności, zamknięć tranzytywnych i zamknięć antytranzytywnych. Typowymi narzędziami tego poznania są macierze: przejść i osiągalności. Powodem wybrania pompy wirowej jest nie tylko jej ważkość i powszechność użycia, ale i specyfika współdziałania jej elementów. Można wśród nich wyróżnić: niezależność, zależność i współzależność. Poszczególnym rozróżnialnym stanom diagnostycznym wyznaczono prawdopodobieństwa ich wystąpienia. Owe prawdopodobieństwa stały się przyczynkiem do kalkulacji entropii struktury i intensywności przejść od stanu zdatności do poszczególnych stanów niezdatności. Wyniki kalkulacji zobrazowano stosownymi wykresami. Odniesiono się do metod bayesowskich i nierozłącznej z nimi „szeregowej struktury niezawodnościowej” wykazując ich wady, spowodowane zwłaszcza uproszczeniami prowadzącymi do fałszywych i niejednoznacznych diagnoz. Prawdopodobieństwa zdatności poszczególnych elementów zróżnicowano doborem adekwatnym im wykładników Weibulla.

3

Chapman-Kolmogorov Equations for a Complete Set of Distinct Reliability States of an Object

Szczepański P., Żurek J.

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

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2018

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Vol. 9, Nr 4 (34)

49--70

EN

The Chapman-Kolmogorov equations indicated in the title are a pretext to demonstrate a mathematically unrecognised truth about the effect of the reliability states of elements (which are generally understood as “subjects”) on the reliability states of a complete set of the same elements, which is called an object. Of importance here are not just the reliability characteristics of individual elements, but the independencies, dependencies and interdependencies between the elements. The relations were described in the language of graph theory. The availability matrix of the language of graph theory was translated to determine the size and probabilities of distinct reliability states of the object, the derivatives of their similarities, and the transition rates adequate to those derivatives. This article continues the research work which identifies the relationship of the properties of a complete set of distinct reliability states of an object with a widely understood theory of systems. The previous papers referred, among others, to: risk, safety, structure entropy, the reliability of the results of checks, and – most of all – technical diagnostics, both in the area of its algorithms and of its optimisation. The object’s serial reliability structure was not assumed in any of those papers, recognising that it would be a serious abuse. The research results were referred to all possible structures of a three-element object. It is believed that by virtue of the block diagrams appropriate to those structures, the readers hereof are provided with a realistic opportunity to practically (and inexpensively) verify the ideas presented here.

PL

W artykule tytułowe „równania Chapmana-Kołmogorowa” są pretekstem do ukazania nieuświadomionej matematycznie prawdy o wpływie stanów diagnostycznych elementów (szeroko pojętych podmiotów) na stany diagnostyczne całego swojego zbioru, nazywanego krótko obiektem. Istotne są tu nie tylko charakterystyki niezawodnościowe poszczególnych elementów, ale przede wszystkim występujące między tymi elementami relacje niezależności, zależności i współzależności. Do opisu tych relacji posłużono się językiem teorii grafów, którego macierz osiągalności przełożono dla potrzeb wyznaczania: liczebności i prawdopodobieństw rozróżnialnych stanów diagnostycznych obiektu, pochodnych rzeczonych prawdopodobieństw i adekwatnych tym pochodnym – intensywności przejść. Niniejszy artykuł jest kontynuacją prac wskazujących na związek właściwości pełnego zbioru rozróżnialnych stanów diagnostycznych obiektu z szeroko pojętą teorią systemów. Wcześniejsze prace odnosiły się m.in. do: ryzyka, bezpieczeństwa, entropii struktury, wiarygodności wyników sprawdzeń i – przede wszystkim – diagnostyki technicznej, tak w obszarze jej algorytmów, jak i optymalizacji. W żadnej z nich nie założono szeregowej struktury niezawodnościowej obiektu. Przykłady analiz odniesiono do wszystkich możliwych struktur konstrukcyjnych obiektu trzyelementowego. Żywi się przekonanie, że wraz z podaniem przystających do tych struktur schematów ideowych stwarza się Czytelnikowi realną możliwość praktycznej (i taniej) weryfikacji przedstawionych przemyśleń.

4

Digraph-building method for finding a set of minimal realizations of 2-D dynamic systems

Markowski K. A., Hryniów K.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2018

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Vol. 66, nr 5

589--597

EN

This paper presents a digraph-building method designed to find the determination of realization of two-dimensional dynamic system. The main differences between the method proposed and other state-of-the-art solutions used include finding a set of realizations (belonging to a defined class) instead of only one realization, and the fact that obtained realizations have minimal size of state matrices. In the article, the proposed method is described, compared to state-of-the-art methods and illustrated with numerical examples. To the best of authors’ knowledge, the method shown in the paper is superior to all other state-of-the-art solutions both in terms of number of solutions and their matrix size. Additionally, MATLAB function for determination of realization based on the set of state matrices is included.

5

Toward Wojda's conjecture on digraph packing

Konarski J., Żak A.

Opuscula Mathematica

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2017

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Vol. 37, no. 4

589--595

EN

Given a positive integer m ≤ n/2, Wojda conjectured in 1985 that if D1 and D2 are digraphs of order n such that [formula] and [formula] then D1 and D2 pack. The cases when m = 1 or m = n/2 follow from known results. Here we prove the conjecture for [formula].

6

Rough Set Theory and Digraphs

Chiaselotti G., Ciucci D., Gentile T., Infusino F.

Fundamenta Informaticae

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2017

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Vol. 153, nr 4

291--325

EN

In this paper we apply rough set theory to information tables induced from finite directed graphs without loops and multiples arcs (digraphs). Specifically, we use the adjacency matrix of a digraph as a particular type of information table. In this way, we are able to explore on digraphs the notions of indiscernibility partitions, lower and upper approximations, generalized core, reducts and discernibility matrix. All these ideas will be exemplified on standard digraph families as well on examples from social networks and patterns of flight routes between airports.

7

Power on digraphs

Peters H., Timmer J., van den Brink R.

Operations Research and Decisions

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2016

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Vol. 26, No. 2

107--125

EN

It is assumed that relations between n players are represented by a directed graph or digraph. Such a digraph is called invariant if there is a link (arc) between any two players between whom there is also a directed path. We characterize a class of power indices for invariant digraphs based on four axioms: Null player, Constant sum, Anonymity, and the Transfer property. This class is determined by 2n – 2 parameters. By considering additional conditions about the effect of adding a directed link between two players, we single out three different, one-parameter families of power indices, reflecting several well- -known indices from the literature: the Copeland score, β- and apex type indices.

8

On arc-coloring of digraphs

Zwonek M.

Opuscula Mathematica

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2006

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Vol. 26, no. 1

185-195

EN

In the paper we deal with the problem of the arc-colouring of some classes of digraphs (tournaments, complete digraphs and products of digraphs).

9

Large minimal irregular digraphs

Dziechcińska-Halamoda Z., Majcher Z., Michael J., Skupień Z.

Opuscula Mathematica

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2003

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Vol. 23

21-24

EN

A digraph is called irregular if its distinct vertices have distinct degree pairs. An irregular digraph is called minimal if the removal of any arc results in a non-irregular digraph. A large minimal irregular digraph Fn of order n is constructed if n is the sum of initial positive integers. It is easily seen that the minimum and maximum sizes among n-vertex irregular digraphs are asymptotic to [formula] and n2, respectively. It appears that the size of Fn is asymptotic to n2, too. Similarly, a minimal irregular oriented graph Hn is constructed such that the size of Hn is asymptotic to 1/2n2 whence it is asymptotically the largest size among n-vertex oriented graphs whether irregular or not.

10

Digraph description of k-interchange technique for optimization over permutations and adaptive algorithm system

Levin M. S.

Foundations of Computing and Decision Sciences

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2001

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Vol. 26, No. 3

225-235

EN

The paper describes a general glance to the use of element exchange techniques for optimization over permutations. A multi-level description of problems is proposed which is a fundamental to understand nature and complexity of optimization problems over permutations (e.g., ordering, scheduling, traveling salesman problem). The description is based on permutation neighborhoods of several kinds (e.g., by improvement of an objective function). Our proposed operational digraph and its kinds can be considered as a way to understand convexity and polynomial solvability for combinatorial optimization problems over permutations. Issues of an analysis of problems and a design of hierarchical heuristics are discussed. The discussion leads to a multi-level adaptive algorithm system which analyzes an individual problem and selects / designs a solving strategy (trajectory).