Instance Created:  April 26, 2002
Number of Cities:  6880
Optimal Value:  21535
Solved:  April 16, 2017

History

Date	Gap	Lower Bound	Tour
10.6.02			21542 - Best of 10 runs of LKH, each with n trials. Total running time 28242 seconds on an AMD Althlon 1900+ processor (1.6 GHz).
26.2.03			21537 - Found by Hung Dinh Nguyen using a parallel hybrid genetic algorithm. The running time was 16033 seconds on a Sun Ultra 80 with four 450-MHz processors (taking the best of five runs).
24.5.06			21535 - Found by Boris Goldengorin, Gerold Jaeger, Paul Molitor, Dirk Richter by a tolerance based variant of LKH using Weixiong Zhang's idea of backbones. The running time was 5327 seconds on a AMD64 4000+ (2.4 GHz)
16.4.17	Optimal	21535 - Concorde (-Z1 -J4), using CPLEX as an LP solver. Wall-clock time for the branch-and-cut search was 2.2 days on a 48-core Intel Xeon E5-2620 @ 2.00GHz cluster; search tree contained 2,649 nodes.

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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