Alternating Sign Matrices and Beyond

James Propp

University of Wisconsin

September 17,
4:15pm
refreshments at 3:45pm
2-338

ABSTRACT 

The solution of the alternating sign matrix by Zeilberger is likely to be only the end of the first chapter of a very long and interesting story. Here are excerpts from three later chapters, with an emphasis on accessible open problems.

One chapter concerns enumeration of ASMs that are invariant under various symmetry groups, and more generally, the enumeration of constrained alternating sign patterns. I'll discuss experimental work on halved ASMs (largely inspired by some still-obscure results of the physicist Tsuchiya).

Another chapter concerns the densely-packed loop representation of ASMs, and a discovery made by Harvard undergraduates Carl Bosley and Lukasz Fidkowski and later proved by M.I.T. undergraduate Ben Wieland: there is a sense in which alternating sign matrices of order $n$ are governed by the symmetry group $D(n)$ (the dihedral group of order $2n$).

A third chapter concerns the matrix condensation process (due to Dodgson) that inspired Mills, Robbins, and Rumsey to invent ASMs in the first place. Variant forms of condensation give rise to new analogues of ASMs. There are no obvious counterparts of the Mills-Robbins-Rumsey conjecture for these analogues, but there are still interesting enumerative phenomena that await explanation.


Speaker's Contact Info: propp(at-sign)math.wisc.edu


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Combinatorics Seminar, Mathematics Department, MIT, sara(at-sign)math.mit.edu

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