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Recursive generation of simple planar quadrangulations with vertices of degree 3 and 4

Mahdieh Hasheminezhad, Brendan D. McKay (2010)

Discussiones Mathematicae Graph Theory

We describe how the simple planar quadrangulations with vertices of degree 3 and 4, whose duals are known as octahedrites, can all be obtained from an elementary family of starting graphs by repeatedly applying two expansion operations. This allows for construction of a linear time generator of all graphs in the class with at most a given order, up to isomorphism.

Sharp edge-homotopy on spatial graphs.

Ryo Nikkuni (2005)

Revista Matemática Complutense

A sharp-move is known as an unknotting operation for knots. A self sharp-move is a sharp-move on a spatial graph where all strings in the move belong to the same spatial edge. We say that two spatial embeddings of a graph are sharp edge-homotopic if they are transformed into each other by self sharp-moves and ambient isotopies. We investigate how is the sharp edge-homotopy strong and classify all spatial theta curves completely up to sharp edge-homotopy. Moreover we mention a relationship between...

Short cycles of low weight in normal plane maps with minimum degree 5

Oleg V. Borodin, Douglas R. Woodall (1998)

Discussiones Mathematicae Graph Theory

In this note, precise upper bounds are determined for the minimum degree-sum of the vertices of a 4-cycle and a 5-cycle in a plane triangulation with minimum degree 5: w(C₄) ≤ 25 and w(C₅) ≤ 30. These hold because a normal plane map with minimum degree 5 must contain a 4-star with w ( K 1 , 4 ) 30 . These results answer a question posed by Kotzig in 1979 and recent questions of Jendrol’ and Madaras.

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