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Paths through inverse limits
Iztok Banič, Matevž Črepnjak, Matej Merhar, Uroš Milutinović, 2011, izvirni znanstveni članek

Opis: In Banič, Črepnjak, Merhar and Milutinović (2010) [2] the authors proved that if a sequence of graphs of surjective upper semi-continuous set-valued functions ▫$f_n : X to 2^X$▫ converges to the graph of a continuous single-valued function ▫$f : X to X$▫, then the sequence of corresponding inverse limits obtained from ▫$f_n$▫ converges to the inverse limit obtained from ▫$f$▫. In this paper a more general result is presented in which surjectivity of ▫$f_n$▫ is not required. The result is also generalized to the case of inverse sequences with non-constant sequences of bonding maps. Finally, these new theorems are applied to inverse limits with tent maps. Among other applications, it is shown that the inverse limits appearing in the Ingram conjecture (with a point added) form an arc.
Ključne besede: mathematics, topology, continua, limits, inverse limits, upper semi-continuous set-valued functions, paths, arcs
Objavljeno: 07.06.2012; Ogledov: 800; Prenosov: 31
URL Povezava na celotno besedilo

3.
Paths through inverse limits
Iztok Banič, Matevž Črepnjak, Matej Merhar, Uroš Milutinović, 2009

Opis: In [I.Banič, M. Črepnjak, M. Merhar, U. Milutinović, Limits of inverse limits, Topology Appl. 157 (2010) 439-450] the authors proved that if a sequence of graphs of surjective upper semi-continuous set-valued functions ▫$f_n: X rightarrow 2^X$▫ converges to the graph of a continuous single-valued function ▫$f: X rightarrow X$▫, then the sequence of corresponding inverse limits obtained from ▫$f_n$▫ converges to the inverse limit obtained from ▫$f$▫. In this paper a more general result is presented in which surjectivity of ▫$f_n$▫ is not required. Also, the result is generalized to the case of inverse sequences with non-constant sequences of bonding maps. Finally, these new theorems are applied to inverse limits with tent maps. Among other applications it is shown that the inverse limits appearing in the Ingram conjecture (with a point added) form an arc.
Ključne besede: matematika, topologija, kontinuumi, limite, inverzne limite, navzgor polzvezne večlične funkcije, poti, loki, mathematics, topology, continua, limits, inverse limits, upper semi-continuous set-valued functions, paths, arcs
Objavljeno: 10.07.2015; Ogledov: 460; Prenosov: 15
URL Povezava na celotno besedilo

4.
5.
NZ-flows in strong products of graphs
Wilfried Imrich, Iztok Peterin, Simon Špacapan, Cun-Quan Zhang, 2010, izvirni znanstveni članek

Opis: Za krepki produkt ▫$G_1 boxtimes G_2$▫ grafov ▫$G_1$▫ in ▫$G_2$▫ dokažemo, da je ▫${mathbb{Z}}_3$▫-pretočno kontraktibilen natanko tedaj, ko ▫$G_1 boxtimes G_2$▫ ni izomorfen ▫$Tboxtimes K_2$▫ (kar poimenujemo ▫$K_4$▫-drevo), kjer je ▫$T$▫ drevo. Sledi, da za ▫$G_1 boxtimes G_2$▫ obstaja NZ 3-pretok, razen če je ▫$G_1 boxtimes G_2$▫ ▫$K_4$▫-drevo. Dokaz je konstruktiven in implicira polinomski algoritem, ki nam vrne NZ 3-pretok, če ▫$G_1 boxtimes G_2$▫ ni ▫$K_4$▫-drevo, oziroma NZ 4-pretok sicer.
Ključne besede: matematika, teorija grafov, celoštevilski pretoki, krepki produkt, poti, cikli, nikjer ničelni pretok, mathematics, graph theory, integer flows, strong product, paths, cycles
Objavljeno: 10.07.2015; Ogledov: 290; Prenosov: 30
URL Povezava na celotno besedilo

6.
On graph identification problems and the special case of identifying vertices using paths
Florent Foucaud, Matjaž Kovše, 2012, objavljeni znanstveni prispevek na konferenci

Opis: V članku uvedemo problem identifikacije s potmi: pokritje z identifikacijskimi potmi grafa ▫$G$▫ je množica poti ▫$mathcal{P}$▫, za katere velja, da vsako vozlišče leži na vsaj eni poti iz ▫$mathcal{P}$▫, in za vsak par vozlišč $u,v$ obstaja pot iz ▫$mathcal{P}$▫, ki vsebuje natanko eno izmed vozlišč ▫$u$▫ in ▫$v$▫. Ta problem je soroden raznim variantam identifikacijskih problemov. Problem pokritja z identifikacijskimi potmi obravnavamo na nekaterih družinah grafov. Izpeljemo optimalne velikosti za pokritja z identifikacijskimi potmi za: poti, cikle, hiperkocke in topološka drevesa ter podamo zgornjo mejo za poljubna drevesa. Podamo tudi spodnje in zgornje meje za minimalno velikost pokritja z identifikacijskimi potmi za poljubne grafe in obravnavamo natančnost mej. Pokažemo, da poljuben povezan graf ▫$G$▫ premore pokritje z identifikacijskimi potmi velikosti kvečjemu ▫$Biglceil frac{2(|V(G)|-1)}{3} Bigrceil$▫. Obravnavamo tudi računsko zahtevnost pripadajočega optimizacijskega problema in pokažemo, da v primeru, ko so dolžine poti iz pokritja fiksne dolžine, sodi problem med APX-polne probleme.
Ključne besede: matematika, teorija grafov, poti, aproksimacija, mathematics, graph theory, test cover, identification, paths, approximation
Objavljeno: 10.07.2015; Ogledov: 305; Prenosov: 26
URL Povezava na celotno besedilo

7.
The number of moves of the largest disc in shortest paths on Hanoi graphs
Simon Aumann, Katharina Götz, Andreas Hinz, Ciril Petr, 2014, izvirni znanstveni članek

Opis: In contrast to the widespread interest in the Frame-Stewart conjecture (FSC) about the optimal number of moves in the classical Tower of Hanoi task with more than three pegs, this is the first study of the question of investigating shortest paths in Hanoi graphs ▫$H_p^n$▫ in a more general setting. Here ▫$p$▫ stands for the number of pegs and ▫$n$▫ for the number of discs in the Tower of Hanoi interpretation of these graphs. The analysis depends crucially on the number of largest disc moves (LDMs). The patterns of these LDMs will be coded as binary strings of length ▫$p-1$▫ assigned to each pair of starting and goal states individually. This will be approached both analytically and numerically. The main theoretical achievement is the existence, at least for all ▫$n \geqslant p(p-2)$▫, of optimal paths where ▫$p-1$▫ LDMs are necessary. Numerical results, obtained by an algorithm based on a modified breadth-first search making use of symmetries of the graphs, lead to a couple of conjectures about some cases not covered by our ascertained results. These, in turn, may shed some light on the notoriously open FSC.
Ključne besede: graph theory, Tower of Hanoi, Hanoi graphs, shortest paths, symmetries, breadth-first search
Objavljeno: 14.08.2017; Ogledov: 385; Prenosov: 28
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