Gauss Code Loops

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Draw a closed loop that crosses itself several times. Draw an arrow on the loop, then follow it, labeling every other intersection with 1, 2, 3, …, until the arrow is reached. Following these steps, every intersection will be labeled once, a fact noticed by Gauss. With additional steps, the Gauss code of the loop can be written, allowing reconstruction of the original diagram.


For orders 3, 4, 5, …, there are 3, 5, 16, 44, 180, … distinct graphs that come from the permutations. For orders 5, 6, and 7, there are 2, 36, and 571 permutations that cannot be drawn as self-intersecting loops due to nonplanarity. Some permutations may have parity issues that will prevent a Gauss code loop representation.


Contributed by: Ed Pegg Jr (March 2011)
Open content licensed under CC BY-NC-SA



Charles Livingston and Jae Choon Cha, "Notation for Knots: Gauss Code."

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