22,952 research outputs found
Knot Graphs
We consider the equivalence classes of graphs induced by the unsigned
versions of the Reidemeister moves on knot diagrams.
Any graph which is
reducible by some finite sequence of these moves, to a graph with no
edges is called a knot graph. We show that the class of knot graphs
strictly contains the set of delta-wye graphs. We prove that the
dimension of the intersection of the cycle and cocycle spaces is an
effective numerical invariant of these classes
Intrinsic Linking and Knotting in Virtual Spatial Graphs
We introduce a notion of intrinsic linking and knotting for virtual spatial
graphs. Our theory gives two filtrations of the set of all graphs, allowing us
to measure, in a sense, how intrinsically linked or knotted a graph is; we show
that these filtrations are descending and non-terminating. We also provide
several examples of intrinsically virtually linked and knotted graphs. As a
byproduct, we introduce the {\it virtual unknotting number} of a knot, and show
that any knot with non-trivial Jones polynomial has virtual unknotting number
at least 2.Comment: 13 pages, 13 figure
Expansions for the Bollobas-Riordan polynomial of separable ribbon graphs
We define 2-decompositions of ribbon graphs, which generalise 2-sums and
tensor products of graphs. We give formulae for the Bollobas-Riordan polynomial
of such a 2-decomposition, and derive the classical Brylawski formula for the
Tutte polynomial of a tensor product as a (very) special case. This study was
initially motivated from knot theory, and we include an application of our
formulae to mutation in knot diagrams.Comment: Version 2 has minor changes. To appear in Annals of Combinatoric
Knot graphs and Gromov hyperbolicity
We define a broad class of graphs that generalize the Gordian graph of knots. These knot graphs take into account unknotting operations, the concordance relation, and equivalence relations generated by knot invariants. We prove that overwhelmingly, the knot graphs are not Gromov hyperbolic, with the exception of a particular family of quotient knot graphs. We also investigate the property of homogeneity, and prove that the concordance knot graph is homogeneous. Finally, we prove that that for any , there exists a knot such that the ball of radius in the Gordian graph centered at contains no connected sum of torus knots
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