Gauss Codes: Difference between revisions

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The Gauss Code of an <math>n</math>-crossing knot or link <math>L</math> is obtained as follows:
The Gauss Code of an <math>n</math>-crossing knot or link <math>L</math> is obtained as follows:


* Number the crossings of $ L$ from 1 to $ n$ in an arbitrary manner.
* Number the crossings of <math>L</math> from 1 to <math>n</math> in an arbitrary manner.
* Order the components of $ L$ is some arbitrary manner.
* Order the components of <math>L</math> is some arbitrary manner.
* Start ``walking'' along the first component of $ L$, taking note of the numbers of the crossings you've gone through. If in a given crossing crossing you cross on the ``over'' strand, write down the number of that crossing. If you cross on the ``under'' strand, write down the negative of the number of that crossing.
* Start "walking" along the first component of <math>L</math>, taking note of the numbers of the crossings you've gone through. If in a given crossing crossing you cross on the "over" strand, write down the number of that crossing. If you cross on the "under" strand, write down the negative of the number of that crossing.
* Do the same for all other components of $ L$ (if any).
* Do the same for all other components of <math>L</math> (if any).


The resulting list of signed integers (in the case of a knot) or list of lists of signed integers (in the case of a link) is called the Gauss Code of <math>L</math>. <code>KnotTheory`</code> has some rudimentary support for Gauss codes:
The resulting list of signed integers (in the case of a knot) or list of lists of signed integers (in the case of a link) is called the Gauss Code of <math>L</math>. <code>KnotTheory`</code> has some rudimentary support for Gauss codes:

Revision as of 19:25, 23 August 2005

The Gauss Code of an -crossing knot or link is obtained as follows:

  • Number the crossings of from 1 to in an arbitrary manner.
  • Order the components of is some arbitrary manner.
  • Start "walking" along the first component of , taking note of the numbers of the crossings you've gone through. If in a given crossing crossing you cross on the "over" strand, write down the number of that crossing. If you cross on the "under" strand, write down the negative of the number of that crossing.
  • Do the same for all other components of (if any).

The resulting list of signed integers (in the case of a knot) or list of lists of signed integers (in the case of a link) is called the Gauss Code of . KnotTheory` has some rudimentary support for Gauss codes:

(For In[1] see Setup)

In[2]:= ?GaussCode

GaussCode[i1, i2, ...] represents a knot via its Gauss Code following the conventions used by the knotilus website, http://srankin.math.uwo.ca/cgi-bin/retrieve.cgi/html/start.html. Likewise GaussCode[l1, l2, ...] represents a link, where each of l1, l2,... is a list describing the code read along one component of the link. GaussCode also acts as a "type caster", so for example, GaussCode[K] where K is is a named knot (or link) returns the Gauss code of that knot.

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