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Edge-connectivity of strong products of graphs
Boštjan Brešar, Simon Špacapan, 2007, original scientific article

Abstract: The strong product ▫$G_1 \boxtimes G_2$▫ of graphs ▫$G_1$▫ and ▫$G_2$▫ is the graph with ▫$V(G_1) \times V(G_2)$▫ as the vertex set, and two distinct vertices ▫$(x_1,x_2)$▫ and ▫$(y_1,y_2)$▫ are adjacent whenever for each ▫$i\in \{1,2\}$▫ either ▫$x_i=y_i$▫ or ▫$x_iy_i \in E(G_i)$▫. In this note we show that for two connected graphs ▫$G_1$▫ and ▫$G_2$▫ the edge-connectivity ▫$\lambda(G_1 \boxtimes G_2)$▫ equals ▫$\min\{\delta(G_1\boxtimes G_2), \lambda(G_1)(|V(G_2)|+2|E(G_2)|), \lambda(G_2)(|V(G_1)|+2|E(G_1)|)\}$▫. In addition, we fully describe the structure of possible minimum edge cut sets in strong products of graphs.
Keywords: mathematics, graph theory, connectivity, strong product, graph product, separating set
Published in DKUM: 31.03.2017; Views: 1447; Downloads: 375
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Maps preserving zero products
J. Alaminos, Matej Brešar, J. Extremera, A. R. Villena, 2009, original scientific article

Abstract: Linearna preslikava ▫$T$▫ iz Banachove algebre ▫$A$▫ v Banachovo algebro ▫$B$▫ ohranja ničelni produkt, če je ▫$T(a)T(b) = 0$▫, kadarkoli je ▫$ab = 0$▫. Glavna tema članka je vprašanje, kdaj je zvezna linearna surjektivna preslikava ▫$T: A to B$▫, ki ohranja ničelni produkt, uteženi homomorfizem. Dokažemo, da to velja za velik razred algeber, ki vključuje grupne algebre. Naša metoda sloni na obravnavi bilinearnih preslikav ▫$phi : A times A to X$▫ (kjer je ▫$X$▫ Banachov prostor) z lastnostjo, da iz ▫$ab=0$▫ sledi ▫$phi(a,b) = 0$▫. Dokažemo, da taka preslikava zadošča ▫$phi(amu, b) = phi(a,mu b)$▫ za vse ▫$a,b in A$▫ in vse ▫$mu$▫ iz zaprtja glede na krepko operatorsko topologijo podalgebre multiplikacijske algebre ▫${mathcal M}(A)$▫ generirane z dvostranko potenčno omejenimi elementi. Ta metoda je uporabna tudi za karakterizacijo odvajanj s pomočjo ničelnega produkta.
Keywords: matematika, teorija operatorjev, grupna algebra, ▫$C^ast$▫-algebra, homomorfizem, uteženi homomorfizem, odvajanje, posplošeno odvajanje, mathematics, operator theory, group algebra, ▫$C^ast$▫-algebra, homomorphism, weighted homomorphism, derivation, generalized derivation, separating map, disjointness preserving map, zero product preserving map, doubly power-bounded element
Published in DKUM: 10.07.2015; Views: 1301; Downloads: 101
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On edge connectivity of direct products of graphs
Xiang-Lan Cao, Špela Brglez, Simon Špacapan, Elkin Vumar, 2011, original scientific article

Abstract: Let ▫$lambda(G)$▫ be the edge connectivity of ▫$G$▫. The direct product of graphs ▫$G$▫ and ▫$H$▫ is the graph with vertex set ▫$V(G times H) = V(G) times V(H)$▫, where two vertices ▫$(u_1,v_1)$▫ and ▫$(u_2,v_2)$▫ are adjacent in ▫$G times H$▫ if ▫$u_1u_2 in E(G)$▫ and ▫$v_1v_2 in E(H)$▫. We prove that ▫$lambda(G times K_n) = min{n(n-1)lambda(G), (n-1)delta(G)}$▫ for every nontrivial graph ▫$G$▫ and ▫$n geqslant 3$▫. We also prove that for almost every pair of graphs ▫$G$▫ and ▫$H$▫ with ▫$n$▫ vertices and edge probability ▫$p$▫, ▫$G times H$▫ is ▫$k$▫-connected, where ▫$k=O((n/log n)^2)$▫.
Keywords: mathematics, graph theory, combinatorial problems, connectivity, direct product, graph product, separating set
Published in DKUM: 01.06.2012; Views: 2320; Downloads: 224
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