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Dynamic Cycles in Edge-Colored Multigraphs

  • Hortensia Galeana-Sánchez,
  • Carlos Vilchis-Alfaro

摘要

Let H be a graph possibly with loops and G be a multigraph without loops. An H-coloring of G is a function \(c: E(G) \rightarrow V(H)\) c : E ( G ) V ( H ) . We will say that G is an H-colored multigraph, whenever we are taking a fixed H-coloring of G. The set of all the edges with end vertices u and v will be denoted by \(E_{uv}\) E uv . We will say that \(W=(v_0,e_0^1, \ldots , e_0^{k_0},v_1,e_1^1,\ldots ,\) W = ( v 0 , e 0 1 , , e 0 k 0 , v 1 , e 1 1 , , \(e_1^{k_1},v_2,\ldots ,v_{n-1},e_{n-1}^1,\ldots ,e_{n-1}^{k_{n-1}},v_n)\) e 1 k 1 , v 2 , , v n - 1 , e n - 1 1 , , e n - 1 k n - 1 , v n ) , where for each i in \(\{0,\ldots ,\) { 0 , , \(n-1\}\) n - 1 } , \(k_i \ge 1\) k i 1 and \(e_i^j \in E_{v_iv_{i+1}}\) e i j E v i v i + 1 for every \(j \in \{1,\ldots , k_i \}\) j { 1 , , k i } , is a dynamic H-walk iff \(c(e_i^{k_i})c(e_{i+1}^1)\) c ( e i k i ) c ( e i + 1 1 ) is an edge in H, for each \(i \in \{0,\ldots ,n-2\}\) i { 0 , , n - 2 } . We will say that a dynamic H-walk is a closed dynamic H-walk whenever \(v_0=v_n\) v 0 = v n and \(c(e_{n-1}^{k_{n-1}})c(e_0^1)\) c ( e n - 1 k n - 1 ) c ( e 0 1 ) is an edge in H. Moreover, a closed dynamic H-walk is called dynamic H-cycle whenever \(v_i\ne v_j\) v i v j , for every \(\{i,j\}\subseteq \{0,\ldots ,v_{n-1}\}\) { i , j } { 0 , , v n - 1 } . In particular, a dynamic H-walk is an H-walk whenever \(k_i=1\) k i = 1 , for every \(i \in \{0,\ldots ,n-1\}\) i { 0 , , n - 1 } , and when H is a complete graph without loops, an H-walk is well known as a properly colored walk. In this work, we study the existence and length of dynamic H-cycles, dynamic H-trails and dynamic H-paths in H-colored multigraphs. To accomplish this, we introduce a new concept of color degree, namely, the dynamic degree, which allows us to extend some classic results, as Ore’s Theorem, for H-colored multigraphs. Also, we give sufficient conditions for the existence of hamiltonian dynamic H-cycles in H-colored multigraphs, and as a consequence, we obtain sufficient conditions for the existence of properly colored hamiltonian cycle in edge-colored multigraphs, with at least \(c\ge 3\) c 3 colors.