Instance Created:  July 29, 2001
Number of Cities:  22,775
Optimal Value:  569,288
Solved:  April 28, 2009
Solution Method:  Concorde

History

Date	Gap	Lower Bound	Tour
8.24.01			569,335 - Found by merging 3 LKH tours (each with n trials). The total time to find the tours was 482,069 seconds on a 500 MHz EV6 Alpha; merging required an additional 279.50 seconds). The best LKH tour had length 569,366.
8.26.01	0.039%	569,115 - Established by Concorde with -C 20 (used 23 nodes in the branch-and-cut tree, 114,751 seconds on a 500 MHz EV6 Alpha).
9.17.01	0.032%		569,295 - Found by morphing and merging 10 LKH tours (each with n trials). The total time to find the tours was 1,654,780 seconds on a 500 MHz EV6 Alpha; morphing the tours required an additional 66.74 seconds and merging the morphed tours required an 14,886.06 seconds). The best LKH tour had length 569,362.
9.30.01	0.030%		569,288 - Found by Keld Helsgaun using variants of his LKH code. The running time was approximately 1 week on a 400 MHz PowerMac G4.

Notes

1. Concorde is our linear-programming based TSP solver.

2. linkern is an implementation of Martin, Otto, and Felten's Chained Lin-Kernighan heuristic. It is included in the Concorde code.

3. LKH is Keld Helsgaun's powerful implementation of the Lin-Kernighan heuristic.

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