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Exact generating function for 2-convex polygons

W R G James, I Jensen and A J Guttmann

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Polygons are described as almost-convex if their perimeter differs from the perimeter of their minimum bounding rectangle by twice their 'concavity index', m. Such polygons are called m-convex polygons and are characterized by having up to m indentations in their perimeter. We first describe how we conjectured the (isotropic) generating function for the case m = 2 using a numerical procedure based on series expansions. We then proceed to prove this result for the more general case of the full anisotropic generating function, in which steps in the x and y directions are distinguished. In doing so, we develop tools that would allow for the case m > 2 to be studied.


PACS

02.10.Ox Combinatorics; graph theory

02.30.Mv Approximations and expansions

02.30.Lt Sequences, series, and summability

MSC

05A15 Exact enumeration problems, generating functions (See also 33Cxx, 33Dxx)

41A58 Series expansions (e.g. Taylor, Lidstone series, but not Fourier series)

51E12 Generalized quadrangles, generalized polygons

Subjects

Mathematical physics

Dates

Issue 5 (8 February 2008)

Received 25 May 2007, in final form 1 November 2007

Published 23 January 2008



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