kernels of mallows models for solving permutation-based problems
DESCRIPTION
PreliminariesTRANSCRIPT
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Kernels of Mallows Models for Solving Permutation-based Problems
Josu Ceberio, Alexander Mendiburu, Jose A. Lozano
Genetic and Evolutionary Computation Conference (GECCO 2015)Madrid, Spain, 11-15 July 2015
Intelligent Systems GroupDepartment of Computer Science and Artificial Intelligence
University of the Basque Country UPV/EHU
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Preliminaries
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Combinatorial optimization problems
Permutation optimization problems
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Permutation optimization problems
Problems whose solutions are naturally
represented as permutations
Travelling Salesman Problem (TSP)
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Recently…A new trend of Estimation of Distribution Algorithms for permutation problems have been proposed
EDAs quicklyInitialize populationWhile stopping criterion is not met
Selected most promising individualsLearn a probability distributionSample new individuals from the distributionUpdate the population
Return the best solution
Mallows
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The Mallows modelDefinition
• A distance-based exponential probability model
• Central permutation
• Spread parameter
• A distance on permutations
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The Mallows modelDefinition
• A distance-based exponential probability model
• Central permutation
• Spread parameter
• A distance on permutations
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The Mallows modelDefinition
• A distance-based exponential probability model
• Central permutation
• Spread parameter
• A distance on permutations
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The Mallows modelKendall’s-τ distance
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Measures the number of pairwise disagreements between and .
1-21-31-41-52-32-42-53-43-54-5
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The Mallows modelCayley distance
Measures the minimum number of swap operations to convert in .
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The Mallows modelLearning
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5 4 1 2 34 2 3 5 11 2 3 5 42 4 3 5 13 1 4 5 22 3 4 1 52 3 4 5 12 5 4 3 11 2 5 4 35 3 1 2 4
Population
Calculate the central permutation- Borda (Kendall’s-τ)- Set median permutation (Cayley)
Estimate the spread parameter - Newton-Raphson
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The Mallows modelSampling
• For both metrics, the distance between and can be decomposed as a sum of terms.
Factorized distribution
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Drawbacks
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These models are unimodal
Often too restrictive
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Drawbacks
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What happens if good fitness solutions are far from each other?
Many works in the literature have proposed using mixtures of models
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Drawbacks
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Many works in the literature have proposed using mixtures of models
Building mixture models implies
costly algorithms
What happens if good fitness solutions are far from each other?
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The proposal:Kernels of Mallows models
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Kernels of Mallows models
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5 4 1 2 34 2 3 5 11 2 3 5 42 4 3 5 13 1 4 5 22 3 4 1 52 3 4 5 12 5 4 3 11 2 5 4 35 3 1 2 4
Population
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Mallows Kernels EDA
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Initialize population with individualsInitialize and
While stopping criterion is not metSelected the most promising individualsDefine Mallows kernels from the selected individualsSample individuals from each kernelUpdate populationUpdate
Return the best solution
There is no learning step
Repeated solutions are discardedExploration / Explotation
trade-off
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Experimental Study
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The question
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Can EDAs based on Kernels of Mallows Models outperformMallows EDA (MEDA) or Generalized Mallows EDA (GMEDA)?
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Experimental Design
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• Algorithms:– Mallows EDA (M)– Generalized Mallows EDA (GM)– Mallows Kernel EDA (K)
• Distances:- Kendall’s-τ- Cayley
Benchmark Problems:- Quadratic Assignment Problem (QAP)- Permutation Flowshop Scheduling Problem (PFSP)
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Experimental DesignThe quadratic assignment problem (QAP)
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Experimental DesignThe quadratic assignment problem (QAP)
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Experimental DesignPermutation Flowshop Scheduling Problem (PFSP)
Total flow time (TFT)
m1m2m3m4
j4j1 j3j2 j5
• jobs• machines • processing times
5 x 4
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Experimental DesignInstances
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• 45 Artificial QAP instances:– Size: 100, 150, 200, 250, 300, 350, 400,
450, 500– 5 instances of each size
• 45 Artificial PFSP instances:– Jobs: 50, 100, 200, 250, 300, 350, 400,
450, 500– Machines: 20– 5 instances of each size
Sampling uniformly at random from
[1,100]
Sampling parameters from Taillard’s
instances: tai80a ,tai80b,
tai100a,…
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Experimental Design
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• Parameter Settings:– Population size: 10n– Selected individuals: n– Selection type: truncation
– and :
0.00 2.00 4.00 6.00 8.00 10.00 12.000.000.100.200.300.400.500.600.700.800.901.00
Kendall’s-τ distance
θ
P(σ0
)
– Sampled individuals: 10n-1– Stopping criterion: 1000n2 evals– 10 repetitions
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.000.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Cayley distance
θ
P(σ0
)
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100 150 200 250 300 350 400 450 5000.000.020.040.060.080.100.120.140.160.18
Cayley, QAP GMMK
Instance size
50 100 200 250 300 350 400 450 5000.040.050.060.070.080.090.100.110.120.13
Kendall, PFSP
Instance size
Experimental StudyARPD Results
50 100 200 250 300 350 400 450 5000.00
0.01
0.02
0.03
0.04Cayley, PFSP
Instance size
100 150 200 250 300 350 400 450 5000.10
0.15
0.20
0.25
0.30
0.35Kendall, QAP
Instance size
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50 100 200 250 300 350 400 450 5000.00
0.01
0.02
0.03
0.04Cayley, PFSP
Instance size
50 100 200 250 300 350 400 450 5000.040.050.060.070.080.090.100.110.120.13
Kendall, PFSP
Instance size100 150 200 250 300 350 400 450 500
0.10
0.15
0.20
0.25
0.30
0.35Kendall, QAP
Instance size
100 150 200 250 300 350 400 450 5000.000.020.040.060.080.100.120.140.160.18
Cayley, QAP GMMK
Instance size
Experimental StudyARPD Results
Statistical AnalysisTwo non-parametric Friedman tests (α=0.05)
• QAP (6 algorithms):• PFSP (6 algorithms):
p-value < 0.001p-value < 0.001
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50 100 200 250 300 350 400 450 5000.00
0.01
0.02
0.03
0.04Cayley, PFSP
Instance size
50 100 200 250 300 350 400 450 5000.040.050.060.070.080.090.100.110.120.13
Kendall, PFSP
Instance size100 150 200 250 300 350 400 450 500
0.10
0.15
0.20
0.25
0.30
0.35Kendall, QAP
Instance size
100 150 200 250 300 350 400 450 5000.000.020.040.060.080.100.120.140.160.18
Cayley, QAP GMMK
Instance size
Experimental StudyARPD Results
Statistical AnalysisTwo non-parametric Friedman tests (α=0.05)
• QAP (6 algorithms):• PFSP (6 algorithms):
Shaffer’s static posthoc – pairwise comparisons
• QAP:
• PFSP:
p-value < 0.001p-value < 0.001
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50 100 200 250 300 350 400 450 5000.0E+00
2.0E+05
4.0E+05
6.0E+05
8.0E+05
1.0E+06
1.2E+06
1.4E+06
1.6E+06
1.8E+06Kendall, PFSP
Instance size100 150 200 250 300 350 400 450 500
0.0E+002.0E+054.0E+056.0E+058.0E+051.0E+061.2E+061.4E+061.6E+061.8E+06
Kendall, QAP
Instance size
100 150 200 250 300 350 400 450 5000.0E+002.0E+044.0E+046.0E+048.0E+041.0E+051.2E+051.4E+051.6E+05
Cayley, QAPGMMK
Instance size50 100 200 250 300 350 400 450 500
0.0E+00
1.0E+04
2.0E+04
3.0E+04
4.0E+04
5.0E+04
6.0E+04Cayley, PFSP
Instance size
Experimental StudyComputational Cost (seconds)
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Conclusions
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Can EDAs based on Kernels of Mallows Models outperformMallows EDA (MEDA) and Generalized Mallows EDA (GMEDA)?
Yes, if they are defined under the Cayley distance
In fact, Kernels of Mallows models under the Cayley distance are the best option in terms
of fitness and computational cost
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Future Work
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Short termUnderstand why similar results are not obtained with Kendall’s-τ
Apply automatic (offline) algorithm configuration: Irace
Study more advanced strategies to adapt θs
Long term
Include other distances such as Ulam or Hamming
Apply to other permutation problems
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Thank you for your
attention!