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A001171 From least significant term in expansion of E( tr (X'*X)^n ), X rectangular and Gaussian. Also number of types of sequential n-swap moves for traveling salesman problem.
(Formerly M3570 N1447)
+0
2
1, 1, 4, 20, 148, 1348, 15104, 198144, 2998656, 51290496 (list; graph; listen)
OFFSET

1,3

COMMENT

Let X be a p X q rectangular matrix with random Gaussian entries. Expand E( tr (X'*X)^n ) as a polynomial in p and q for fixed n. Sequence gives coefficient of least significant term in polynomial.

There should be a reference to a paper by Guy et al. (?) that gives a formula.

An n-swap move consists of the removal of n edges and addition of n different edges which result in a new tour. A sequential n-swap is one in which the union of the n removed and n added edges forms a single cycle. The type can be characterized by how the n segments of the original tour formed by the removal are reassembled.

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

P. J. Hanlon, R. P. Stanley and J. R. Stembridge, Some combinatorial aspects of the spectra of normally distributed random matrices. Hypergeometric functions on domains of positivity, Jack polynomials and applications (Tampa, FL, 1991), 151-174, Contemp. Math., 138, Amer. Math. Soc., Providence, RI, 1992.

David L. Applegate, Robert E. Bixby, Vasek Chvatal and William J. Cook, The Traveling Salesman Problem: A Computational Study, Princeton UP, 2006, Table 17.1, p. 535 (has 1358 instead of 1348 for n = 6)

LINKS

Keld Helsgaun, An Effective Implementation of K-opt Movesfor the Lin-Kernighan TSP Heuristic.

FORMULA

Hanlon et al. give a formula (it would be nice to give it here).

A complicated formula from Hanlon is given on page 23 of Helsgaun. - Rob Pratt (Rob.Pratt(AT)sas.com), Mar 30 2007

CROSSREFS

Cf. A061714.

Sequence in context: A144009 A117887 A082988 this_sequence A167018 A094070 A119022

Adjacent sequences: A001168 A001169 A001170 this_sequence A001172 A001173 A001174

KEYWORD

nonn,nice

AUTHOR

C. L. Mallows (colinm(AT)research.avayalabs.com)

EXTENSIONS

Additional comments from David Applegate (david(AT)research.att.com), Jun 21 2001

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Last modified December 15 00:47 EST 2009. Contains 170825 sequences.


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