# discrete CATS seminar

Date:

09/28/2020 - 2:00pm to 3:00pm

Location:

Zoom

Speaker(s) / Presenter(s):

Gábor Hetyei (University of North Carolina - Charlotte)

**Title:**Rational links represented by reduced alternating diagrams

**Abstract:**In knot theory, a rational link may be represented by any of the (infinitely) many link diagrams corresponding to various continued fraction expansions of the same rational number. The continued fraction expansion of the rational number in which all signs are the same is called a nonalternating form and the diagram corresponding to it is a reduced alternating link diagram, which is minimum in terms of the number of crossings in the diagram. Famous formulas exist in the literature for the braid index of a rational link by Murasugi and for its HOMFLY polynomial by Lickorish and Millet, but these rely on a special continued fraction expansion of the rational number in which all partial denominators are even (called all-even form}). In this talk we present an algorithmic way to transform a continued fraction given in nonalternating form into the all-even form. Using this method we derive formulas for the braid index and the HOMFLY polynomial of a rational link in terms of its reduced alternating form, or equivalently the nonalternating form of the corresponding rational number.

This is joint work with Yuanan Diao and Claus Ernst. The talk will define and explain all terms, with a general audience in mind.

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