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Iterated Local Search (ILS) for the Quadratic Assignment Problem (QAP) Tim Daniëlse en Vincent Delvigne
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QAP
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QAP (2)
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Complexity
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Iterated Local Search
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Iterated Local Search (2) Generate Initial Solution – No known, well performing construction algorithm – Randomized assignment
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Iterated Local Search (3)
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Iterated Local Search (4)
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Iterated Local Search (5) Acceptance Criterion – standard criterion: accept only improvements – varies among the algorithm-variants
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QAP instance classes QAPLIB benchmark library 4 instance classes: – randomly generated (class i) – Manhattan distance matrix (class ii) – real-life instances (class iii) – random, resembling real-life (class iv)
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QAP instance classes (2)
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Analysis of search space
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Analysis of search space (2)
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Analysis of search space (3)
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Distance-Fitness Correlation
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Distance-Fitness Correlation (2)
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Stagnation Detection Empirical run-time distribution (RTD) RTD develops below exponential distribution (stagnation) – perform restart
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Algorithm Variations Soft Restarts – Use of history – Random new solution. Random Walk (RW) – Accept answer regardless of improvement – Combination with default “Better” might improve even more
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Algorithm Variations (2)
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Algorithm Variations (3)
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Algorithm Variations (4)
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Algorithm Comparison
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Algorithm Comparison (2)
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Algorithm Comparison (3)
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Evolutionary Variant Variant of the Evolutionary Strategy. Optimized Local Search Different parameter settings
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Evolutionary Variant (3)
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Conclusions Fitness-Distance Correlation analysis ILS runtime analysis Acceptance Criteria analysis ES-MN best performing algorithm.
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References Stutzle, Thomas (2006): Iterated Local Search for the Quadratic Assignment Problem. European Journal of Operational Research 174 (3), 1519-1539.
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