vehicle routing problem אליאור זיברטדרור חבלין. classical vehicle routing n...
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VEHICLE ROUTING PROBLEM
דרור חבליןאליאור זיברט
Classical Vehicle RoutingClassical Vehicle Routing
n customers must be served from a single depot utilizing vehicle with capacity Q for delivering goods
Each customer requires a quantity qi ≤ Q of goods
Customer orders cannot be split
Additional FeaturesAdditional FeaturesDepotsDepots– Multiple locationsMultiple locations
VehiclesVehicles– Multiple vehicle types Multiple vehicle types
and capacitiesand capacities– Release, maximum and Release, maximum and
down timesdown timesCustomersCustomers– Time windows (soft or Time windows (soft or
hard)hard)– Accessibility restrictionsAccessibility restrictions– PriorityPriority– Pickup and deliveryPickup and delivery
RoutesRoutes– Maximum timeMaximum time– Link costsLink costs
Objective Functions– Minimize total traveled
distance– Minimize total traveled
time– Minimize number of
vehicles– Maximize quality of
service – Multiple objective
functions
How Can It Be SolvedHow Can It Be Solved??? ??? Heuristics that Grow Fragments– Nearest neighbor– Double-ended nearest
neighbor– Multiple fragment
heuristicHeuristics that Grow Tours– Nearest addition– Farthest addition– Random addition
Heuristics Based on Trees– Minimum spanning tree– Christofides heuristic– Fast recursive
partitioning
AND MANY MORE
Ant Colony Optimization
(ACO)
OUR CHOICE OF ALGORITHEM
Ants (blind) navigate from nest to food sourceShortest path is discovered via pheromone trails– each ant moves at random– pheromone is deposited on path– ants detect lead ant’s path, inclined to follow– more pheromone on path increases probability
of path being followed
ACO Concepts
ACO SystemACO SystemVirtual “trail” accumulated on path segmentsStarting node selected at randomPath selected at random– based on amount of “trail” present on possible
paths from starting node– higher probability for paths with more “trail”
Ant reaches next node, selects next pathContinues until reaches starting nodeFinished “tour” is a solution
ACO System, cont.ACO System, cont.A completed tour is analyzed for optimality“Trail” amount adjusted to favor better solutions– better solutions receive more trail– worse solutions receive less trail– higher probability of ant selecting path that is part
of a better-performing tourNew cycle is performedRepeated until most ants select the same tour on every cycle (convergence to solution)
ANT ALGORITHEM
The AlgorithmAt the beginning of the search process, a constant amount of pheromone is assigned to all arcs. When located at a node i an ant k uses the pheromone trail to compute the probability of choosing j as the next node:
α - is a weight function based on arc cost etc..β – is a weight function base on arc lengthi When all ants have comleted a tour each ant compute the quantity per unit of length , the pheromone value changes as follows:
By using this rule, the probability increases that forthcoming ants will use this arc.
kiN
ijijij tnt )()(
m
k
kijij
1
Our Code Design :
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