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Weighted wiener indices of molecular graphs with application to alkenes and alkadienes
Simon Brezovnik, Niko Tratnik, Petra Žigert Pleteršek, 2021, izvirni znanstveni članek

Opis: There exist many topological indices that are calculated on saturated hydrocarbons since they can be easily modelled by simple graphs. On the other hand, it is more challenging to investigate topological indices for hydrocarbons with multiple bonds. The purpose of this paper is to introduce a simple model that gives good results for predicting physico-chemical properties of alkenes and alkadienes. In particular, we are interested in predicting boiling points of these molecules by using the well known Wiener index and its weighted versions. By performing the non-linear regression analysis we predict boiling points of alkenes and alkadienes.
Ključne besede: weighted Wiener index, alkenes, alkadienes, boiling point
Objavljeno v DKUM: 30.05.2024; Ogledov: 56; Prenosov: 3
.pdf Celotno besedilo (1,12 MB)
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Szeged-like entropies of graphs
Matthias Dehmer, Frank Emmert-Streib, Niko Tratnik, Petra Žigert Pleteršek, 2022, izvirni znanstveni članek

Ključne besede: Szeged entropy, Mostar entropy, PI entropy, cut method, quotient graphs, sensitivity of a topological descriptor
Objavljeno v DKUM: 20.05.2024; Ogledov: 87; Prenosov: 2
.pdf Celotno besedilo (3,17 MB)
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A method for computing the edge-Hosoya polynomial with application to phenylenes
Martin Knor, Niko Tratnik, 2023, izvirni znanstveni članek

Opis: The edge-Hosoya polynomial of a graph is the edge version of the famous Hosoya polynomial. Therefore, the edge-Hosoya polynomial counts the number of (unordered) pairs of edges at distance $k \ge 0$ in a given graph. It is well known that this polynomial is closely related to the edge-Wiener index and the edge-hyper-Wiener index. As the main result of this paper, we greatly generalize an earlier result by providing a method for calculating the edge-Hosoya polynomial of a graph $G$ which is obtained by identifying two edges of connected bipartite graphs $G_1$ and $G_2$. To show how the main theorem can be used, we apply it to phenylene chains. In particular, we present the recurrence relations and a linear time algorithm for calculating the edge-Hosoya polynomial of any phenylene chain. As a consequence, closed formula for the edge-Hosoya polynomial of linear phenylene chains is derived.
Ključne besede: edge-Hosoya polynomial, graphs, phenylenes
Objavljeno v DKUM: 15.04.2024; Ogledov: 105; Prenosov: 168
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Generalized cut method for computing Szeged-like polynomials with applications to polyphenyls and carbon nanocones
Simon Brezovnik, Niko Tratnik, 2023, izvirni znanstveni članek

Opis: Szeged, Padmakar-Ivan (PI), and Mostar indices are some of the most investigated distance-based Szeged-like topological indices. On the other hand, the polynomials related to these topological indices were also introduced, for example the Szeged polynomial, the edge- Szeged polynomial, the PI polynomial, the Mostar polynomial, etc. In this paper, we introduce a concept of the general Szeged-like polynomial for a connected strength-weighted graph. It turns out that this concept includes all the above mentioned polynomials and also infinitely many other graph polynomials. As the main result of the paper, we prove a cut method which enables us to efficiently calculate a Szeged-like polynomial by using the corresponding polynomials of strength-weighted quotient graphs obtained by a partition of the edge set that is coarser than ▫$\Theta^*$▫-partition. To the best of our knowledge, this represents the first implementation of the famous cut method to graph polynomials. Finally, we show how the deduced cut method can be applied to calculate some Szeged-like polynomials and corresponding topological indices of para-polyphenyl chains and carbon nanocones.
Ključne besede: graph theory, carbon nanocone, topological indices
Objavljeno v DKUM: 25.03.2024; Ogledov: 162; Prenosov: 3
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Outerplane bipartite graphs with isomorphic resonance graphs
Simon Brezovnik, Zhongyuan Che, Niko Tratnik, Petra Žigert Pleteršek, 2024, izvirni znanstveni članek

Opis: We present novel results related to isomorphic resonance graphs of 2-connected outerplane bipartite graphs. As the main result, we provide a structure characterization for 2-connected outerplane bipartite graphs with isomorphic resonance graphs. Three additional characterizations are expressed in terms of resonance digraphs, via local structures of inner duals, as well as using distributive lattices on the set of order ideals of posets defined on inner faces of 2-connected outerplane bipartite graphs.
Ključne besede: distributive lattice, inner dual, isomorphic resonance graphs, order ideal, 2-connected outerplane bipartite graph
Objavljeno v DKUM: 29.02.2024; Ogledov: 203; Prenosov: 8
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The multivariable Zhang-Zhang polynomial of phenylenes
Niko Tratnik, 2023, izvirni znanstveni članek

Opis: The Zhang-Zhang polynomial of a benzenoid system is a well-known counting polynomial that was introduced in 1996. It was designed to enumerate Clar covers, which are spanning subgraphs with only hexagons and edges as connected components. In 2018, the generalized Zhang-Zhang polynomial of two variables was defined such that it also takes into account 10-cycles of a benzenoid system. The aim of this paper is to introduce and study a new variation of the Zhang-Zhang polynomial for phenylenes, which are important molecular graphs composed of 6-membered and 4-membered rings. In our case, Clar covers can contain 4-cycles, 6-cycles, 8-cycles, and edges. Since this new polynomial has three variables, we call it the multivariable Zhang-Zhang (MZZ) polynomial. In the main part of the paper, some recursive formulas for calculating the MZZ polynomial from subgraphs of a given phenylene are developed and an algorithm for phenylene chains is deduced. Interestingly, computing the MZZ polynomial of a phenylene chain requires some techniques that are different to those used to calculate the (generalized) Zhang-Zhang polynomial of benzenoid chains. Finally, we prove a result that enables us to find the MZZ polynomial of a phenylene with branched hexagons.
Ključne besede: Zhang-Zhang polynomial, phenylene, Clar cover, Kekulé structure
Objavljeno v DKUM: 09.02.2024; Ogledov: 240; Prenosov: 8
.pdf Celotno besedilo (719,26 KB)
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A new alternative to Szeged, Mostar, and PI polynomials : the SMP polynomials
Martin Knor, Niko Tratnik, 2023, izvirni znanstveni članek

Opis: Szeged-like topological indices are well-studied distance-based molecular descriptors, which include, for example, the (edge-)Szeged index, the (edge-)Mostar index, and the (vertex-)PI index. For these indices, the corresponding polynomials were also defined, i.e., the (edge-)Szeged polynomial, the Mostar polynomial, the PI polynomial, etc. It is well known that, by evaluating the first derivative of such a polynomial at x = 1, we obtain the related topological index. The aim of this paper is to introduce and investigate a new graph polynomial of two variables, which is called the SMP polynomial, such that all three vertex versions of the above-mentioned indices can be easily calculated using this polynomial. Moreover, we also define the edge-SMP polynomial, which is the edge version of the SMP polynomial. Various properties of the new polynomials are studied on some basic families of graphs, extremal problems are considered, and several open problems are stated. Then, we focus on the Cartesian product, and we show how the (edge-)SMP polynomial of the Cartesian product of n graphs can be calculated using the (weighted) SMP polynomials of its factors.
Ključne besede: SMP polynomial, edge-SMP polynomial, Cartesian product, Szeged index, Mostar index, PI index
Objavljeno v DKUM: 09.02.2024; Ogledov: 202; Prenosov: 15
.pdf Celotno besedilo (320,27 KB)
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Szeged and Mostar root-indices of graphs
Simon Brezovnik, Matthias Dehmer, Niko Tratnik, Petra Žigert Pleteršek, 2023, izvirni znanstveni članek

Opis: Various distance-based root-indices of graphs are introduced and studied in the present article. They are obtained as unique positive roots of modified graph polynomials. In particular, we consider the Szeged polynomial, the weighted-product Szeged polynomial, the weighted-plus Szeged polynomial, and the Mostar polynomial. We derive closed formulas of these polynomials for some basic families of graphs. Consequently, we provide closed formulas for some root-indices and examine the convergence of sequences of certain root-indices. Moreover, some general properties of studied root-indices are stated. Finally, numerical results related to discrimination power, correlations, structure sensitivity, and abruptness of root-indices are calculated, interpreted, and compared to already known similar descriptors.
Ključne besede: Szeged index, Szeged polynomial, Mostar polynomial, root-index, discrimination power, sensitivity
Objavljeno v DKUM: 18.08.2023; Ogledov: 393; Prenosov: 44
.pdf Celotno besedilo (535,31 KB)
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Resonančni grafi nekaterih dvodelnih zunajravninskih grafov in posplošena metoda prerezov : doktorska disertacija
Simon Brezovnik, 2022, doktorska disertacija

Opis: V doktorski disertaciji se najprej ukvarjamo z resonančnimi grafi katakondenziranih sodih obročnih sistemov (CERS-ov) in njihovo povezavo z marjetičnimi kockami. V nadaljevanju razvijemo posplošeno metodo prerezov, ki omogoča izračun različnih topoloških indeksov (Wienerjevega indeksa dvojno vozliščno-uteženega grafa, Schultzevega indeksa ter indeksov tipa Szeged). V uvodnem poglavju so predstavljeni nekateri že znani rezultati v povezavi z resonančnimi grafi in posplošeno metodo prerezov. Prav tako v nekaj stavkih napovemo rezultate, ki sledijo v nadaljevanju. V drugem poglavju zapišemo osnovne definicije, ki se dotikajo področja teorije grafov in so potrebne za razumevanje osrednjega dela. V tretjem poglavju predstavimo vse obravnavane kemijske strukture in grafe, ki modelirajo te strukture. Najprej obravnavamo benzenoidne sisteme, zatem opišemo CERS-e, fenilene in koronoide. V četrtem poglavju definiramo resonančni graf in pojasnimo povezavo med Kekuléjevimi strukturami in popolnimi prirejanji grafa. Nadalje zapišemo algoritem, ki omogoča iskanje resonančnega grafa poljubnega CERS-a, temelji pa na binarnem kodiranju njegovih popolnih prirejanj. Zatem se ukvarjamo tudi z raziskovanjem CERS-ov, ki imajo izomorfne resonančne grafe. Dobljene rezultate nato uporabimo na fenilenih in tako dobimo zvezo med njihovimi resonančnimi grafi in resonančnimi grafi katakondenziranih benzenoidnih grafov. Na koncu poglavja predstavimo definicijo marjetične kocke in karakteriziramo CERS-e, katerih resonančni grafi so marjetične kocke. V petem poglavju so predstavljeni topološki indeksi, ki temeljijo na razdaljah v grafu oziroma na stopnjah vozlišč. Nadalje predstavimo krepko utežene grafe in na njih definiramo indekse tipa Szeged. V zaključku poglavja predstavimo model, s katerim obravnavamo odvisnost med vrelišči alkenov in alkadienov ter povezavno-uteženimi Wienerjevimi indeksi. Pri tem izvedemo nelinearno regresijsko analizo. V šestem poglavju definiramo kvocientni graf poljubnega povezanega grafa. V nadaljevanju predstavimo posplošeno metodo prerezov in dokažemo, da lahko le-to uporabimo tudi za izračun Schultzevega in Gutmanovega indeksa. Rezultate uporabimo na fenilenih in nekaterih drugih grafovskih družinah. Na koncu šestega poglavja razvijemo posplošeno metodo prerezov za topološke indekse tipa Szeged in zapišemo formulo za izračun teh indeksov za poljuben krepko uteženi graf. Nazadnje ponudimo še nekaj zgledov uporabe izpeljane metode za različne molekularne grafe.
Ključne besede: Djoković-Winklerjeva relacija, resonančni graf, benzenoidni sistem, fenilen, CERS, Kekuléjeva struktura, popolno prirejanje, marjetična kocka, kvocientni graf, topološki indeks, Wienerjev indeks, Gutmanov indeks, Schultzev indeks, topološki indeksi tipa Szeged, posplošena metoda prerezov
Objavljeno v DKUM: 27.07.2022; Ogledov: 913; Prenosov: 82
.pdf Celotno besedilo (2,40 MB)

Računanje Wienerjevega indeksa uteženega grafa z združevanjem ?*-razredov
Simon Brezovnik, 2018, magistrsko delo

Opis: Wienerjev indeks igra pomembno vlogo pri poznavanju kemijskih in fizikalnih lastnosti različnih spojin. Predstavlja vsoto razdalj med vsemi neurejenimi pari vozlišč znotraj grafa. Uteženi graf je graf skupaj s funkcijo, ki vsakemu vozlišču predpiše realno število, imenovano utež. Magistrsko delo obravnava računanje Wienerjevega indeksa uteženega grafa s pomočjo reduciranja na posebno skupino grafov, tj. kvocientne grafe in nadaljnje redukcije kvocientnih grafov na enostavnejše grafe. V prvem delu predstavimo nekaj osnovnih definicij in ugotovitev teorije grafov. Zapišemo osnovno definicijo Wienerjevega indeksa in njegovo razširitev na utežene grafe. Spoznamo Djoković-Winklerjevo relacijo in njeno tranzitivno zaprtje. Ob koncu prvega dela spoznamo definicijo delne kocke in zapišemo njeno novo karakterizacijo. Osrednji del magistrske naloge podaja novi metodi za izračun Wienerjevega indeksa nekaterih uteženih grafov. Glavni izrek povezuje izračun Wienerjevega indeksa uteženega grafa z vsoto Wienerjevih indeksov uteženih kvocientnih grafov prvotnega grafa po vseh Θ^∗-razredih, kjer Θ^∗ predstavlja tranzitivno zaprtje Djoković-Winklerjeve relacije. V zadnjem delu predstavimo uporabo zgoraj omenjenega izreka na posebni družini grafov G_n, na benzenoidnih sistemih ter na linearnih fenilenih F_n.
Ključne besede: Wienerjev indeks, delna kocka, uteženi graf, kvocientni graf, Djoković-Winklerjeva relacija, tranzitivno zaprtje
Objavljeno v DKUM: 24.09.2018; Ogledov: 1053; Prenosov: 133
.pdf Celotno besedilo (1,00 MB)

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