Vehicle Routing & Job Shop Scheduling: What’s the Difference?
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Vehicle Routing Vehicle Routing & & Job Shop Job Shop Scheduling: Scheduling: What’s the What’s the Difference? Difference? ICAPS’03, June 13, 2003 J. Christopher Beck, Patrick Prosser, & J. Christopher Beck, Patrick Prosser, & Evgeny Selensky Evgeny Selensky Dept. of Computing Science Dept. of Computing Science University of Glasgow University of Glasgow {pat,evgeny}@dcs.gla.ac.uk {pat,evgeny}@dcs.gla.ac.uk Cork Constraint Cork Constraint Computation Centre Computation Centre University College Cork University College Cork [email protected] [email protected]
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ICAPS’03, June 13, 2003. Vehicle Routing & Job Shop Scheduling: What’s the Difference?. J. Christopher Beck, Patrick Prosser, & Evgeny Selensky. Cork Constraint Computation Centre University College Cork [email protected]. Dept. of Computing Science University of Glasgow - PowerPoint PPT Presentation
Transcript of Vehicle Routing & Job Shop Scheduling: What’s the Difference?
Vehicle Routing & Vehicle Routing & Job Shop Scheduling: Job Shop Scheduling: What’s the Difference?What’s the Difference?
ICAPS’03, June 13, 2003
J. Christopher Beck, Patrick Prosser, & Evgeny SelenskyJ. Christopher Beck, Patrick Prosser, & Evgeny Selensky
Dept. of Computing ScienceDept. of Computing Science
University of Glasgow University of Glasgow
{pat,evgeny}@dcs.gla.ac.uk{pat,evgeny}@dcs.gla.ac.uk
Cork Constraint Computation CentreCork Constraint Computation Centre
University College Cork University College Cork
[email protected]@4c.ucc.ie
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Old Solutions for New ProblemsOld Solutions for New Problems
We have strong techniques to solve hard problems
Use them! – use existing problem models and solution
techniques to solve a new problemCommon approach in research and in
practice– SAT, IP, CP, etc
If you have a hammer, …
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A Nice Idea, ButA Nice Idea, But
New problems don’t fit exactly the old models
New problems look “strange”– Scheduling with 0 duration activities– Routing with 0 travel time
How will solution techniques work?
… is the problem really a nail?
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Get the Picture?Get the Picture?
ExistingProblemModels
Real-WorldProblem
+ ?
?
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This PaperThis Paper
Basic Question– How does existing solution technology cope with
changed characteristics?Basic Approach
– Create problems “between” JSP & VRP– Compare the relative performance of routing and
scheduling solution techniques– What problem characteristics are important to the
solution techniques?More in talk than in the paper
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Vehicle Routing ProblemVehicle Routing Problem
T1
T2T3
Make a set of deliveries (visits) with a set of vehicles– Vehicles have limited
capacity– Visits have time
windows– Minimize total
distance traveled
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R1
R0
R1
R0 R2
R2 R0
R1 R2
R1
R2
R0
R2
R1 R1
R0 R0 R0
R1
R2R2
makespan
Job Shop Scheduling Problem (JSP)Job Shop Scheduling Problem (JSP)
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Off-the-Shelf Solution TechnologyOff-the-Shelf Solution Technology
VRP: ILOG Dispatcher– First Solution: Savings Heuristic– Improvement: Guided Local Search
JSP: ILOG Scheduler– Constructive CP tree-search
• Slack-based heuristics
– Strong constraint propagation• Edge-finding, precedence graph
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Evaluating the TechnologyEvaluating the Technology
Cx: cost of solution found by technology x with fixed time limit (10 minutes)
> 1: routing technology is better < 1: scheduling technology is better
rout
sched
C
C
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JSP JSP VRP Transformation VRP Transformation
[Beck et al. 2002] We can transform JSPs to VRPs
and vice versaScheduling technology is poor
on reformulated VRPsRouting technology is poor on
reformulated JSPs– Can’t find first solutions due to
precedence constraints!
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CharacteristicsCharacteristics
What are the problem characteristics that lead to this difference?Ideas:
– Alternative resources– Optimization criteria– Precedence constraints– (3 more not really discussed here)
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From VRPFrom VRP
VRP
?
?
?
?
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From JSPFrom JSP
JSP
+
?
?
?
?
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Alternative ResourcesAlternative Resources
VRP: many (e.g., 25)JSP: few (1, 4, 8)
Savings can’t solve ~70% of problems with 2 alternatives– Only problems solved by
both are included
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Alternative Resources: VRPAlternative Resources: VRP
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Alternative Resources: JSPAlternative Resources: JSP
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Optimization CriteriaOptimization Criteria
VRP: total travelJSP: makespan
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Optimisation Criteria: VRPOptimisation Criteria: VRP
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Optimisation Criteria: JSPOptimisation Criteria: JSP
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Precedence ConstraintsPrecedence Constraints
VRP: noneJSP: paths of totally
ordered activities
Savings can’t find first solution– Start with scheduling
solution
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Precedence Constraints: VRPPrecedence Constraints: VRP
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Precedence Constraints: JSPPrecedence Constraints: JSP
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Experimental SummaryExperimental Summary
VRP JSP
Alt Res Alt Res
Precedence Cts Precedence Cts
Opt. Makespan Opt. Total Travel
scheduling performance
routing performance
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Other CharacteristicsOther Characteristics
Smaller impactTemporal Slack
slack = scheduling performanceVehicle Resource Capacity
– Like alternative resourcesActivity duration to transition time ratio
– VRP: ratio = routing performance– JSP: ratio = scheduling performance
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ConclusionsConclusions
Try scheduling technology on VRP with– makespan minimization (strong propagation?)– complex temporal constraints
Try routing technology on JSP with– total time minimization (weak propagation?)– few temporal constraints (open shop?)
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ConclusionsConclusions
Even isolated changes in problem characteristics change the best choice of off-the-shelf problem model
Understanding this is important to extending the scope of optimisation techniques to– new problems – new people
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Alternative ResourcesAlternative Resources
