18,241 research outputs found
On embeddings in cycles
We prove several exact results for the dilation of well-known interconnection networks in cycles, namely : for complete -level -ary trees, for -dimensional hypercubes, for 3-dimensional meshes (where is an -vertex path) and for 2-dimensional ordinary, cylindrical and toroidal meshes, respectively. The last results solve three remaining open problems of the type , where and are paths or cycles. The previously known dilations are: , and , if , otherwise . The proofs of the above stated results are based on the following technique. We find a suficient condition for a graph which assures the equality . We prove that trees, X-trees, meshes, hypercubes, pyramides and tree of meshes satisfy the condition. Using known optimal dilations of complete trees, hypercubes and 2- and 3-dimensional meshes in path we get the above exact result
Some Triangulated Surfaces without Balanced Splitting
Let G be the graph of a triangulated surface of genus . A
cycle of G is splitting if it cuts into two components, neither of
which is homeomorphic to a disk. A splitting cycle has type k if the
corresponding components have genera k and g-k. It was conjectured that G
contains a splitting cycle (Barnette '1982). We confirm this conjecture for an
infinite family of triangulations by complete graphs but give counter-examples
to a stronger conjecture (Mohar and Thomassen '2001) claiming that G should
contain splitting cycles of every possible type.Comment: 15 pages, 7 figure
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