com.graphhopper.jsprit.core.algorithm.acceptor

Class SchrimpfAcceptance

java.lang.Object

com.graphhopper.jsprit.core.algorithm.acceptor.SchrimpfAcceptance

All Implemented Interfaces:

SolutionAcceptor, AlgorithmStartsListener, IterationStartsListener, VehicleRoutingAlgorithmListener

public class SchrimpfAcceptance
extends Object
implements SolutionAcceptor, IterationStartsListener, AlgorithmStartsListener

ThresholdAcceptance-Function defined by Schrimpf et al. (2000).

The idea can be described as follows: Most problems do not only have one unique minimum (maximum) but a number of local minima (maxima). To avoid to get stuck in a local minimum at the beginning of a search this threshold-acceptance function accepts also worse solution at the beginning (in contrary to a greedy approach which only accepts better solutions), and converges to a greedy approach at the end.
The difficulty is to define (i) an appropriate initial threshold and (ii) a corresponding function describing how the threshold converges to zero, i.e. the greedy threshold.

ad i) The initial threshold is determined by a random walk through the search space. The random walk currently runs with the following algorithm: src/main/resources/randomWalk.xml. It runs as long as it is specified in nuOfWarmupIterations. In the first iteration or walk respectively the algorithm generates a solution. This solution in turn is the basis of the next walk yielding to another solution value ... and so on. Each solution value is memorized since the initial threshold is essentially a function of the standard deviation of these solution values. To be more precise: initial threshold = stddev(solution values) / 2.

ad ii) The threshold of iteration i is determined as follows: threshold(i) = initialThreshold * Math.exp(-Math.log(2) * (i / nuOfTotalIterations) / alpha) To get a better understanding of the threshold-function go to Wolfram Alpha and plot the following line (just copy and paste it into Wolfram's console: www.wolframalpha.com):

100. * exp(-log(2)* (x/1000) / 0.1) (x from 0 to 1000) (y from 0 to 100)

with
initialThreshold = 100
nuOfTotalIter = 1000
alpha = 0.1
x corresponds to i iterations and
y to the threshold(i)

Gerhard Schrimpf, Johannes Schneider, Hermann Stamm- Wilbrandt, and Gunter Dueck (2000). Record breaking optimization results using the ruin and recreate principle. Journal of Computational Physics, 159(2):139 – 171, 2000. ISSN 0021-9991. doi: 10.1006/jcph.1999. 6413. URL http://www.sciencedirect.com/science/article/ pii/S0021999199964136

Author:

schroeder

Constructor Summary

Constructors

Constructor and Description
SchrimpfAcceptance(int solutionMemory, double alpha)

Method Summary

Modifier and Type	Method and Description
boolean	acceptSolution(Collection<VehicleRoutingProblemSolution> solutions, VehicleRoutingProblemSolution newSolution) Accepts solution or not, and returns true if a new solution has been accepted.
boolean	acceptSolution(VehicleRoutingProblemSolution solution, VehicleRoutingProblemSolution newSolution)
double	getInitialThreshold()
void	incIteration()
void	informAlgorithmStarts(VehicleRoutingProblem problem, VehicleRoutingAlgorithm algorithm, Collection<VehicleRoutingProblemSolution> solutions)
void	informIterationStarts(int i, VehicleRoutingProblem problem, Collection<VehicleRoutingProblemSolution> solutions)
void	setInitialThreshold(double initialThreshold) Sets initial threshold.
void	setMaxIterations(int maxIteration)
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

SchrimpfAcceptance

public SchrimpfAcceptance(int solutionMemory,
                          double alpha)

Method Detail

acceptSolution

public boolean acceptSolution(Collection<VehicleRoutingProblemSolution> solutions,
                              VehicleRoutingProblemSolution newSolution)

Description copied from interface: SolutionAcceptor

Accepts solution or not, and returns true if a new solution has been accepted.

If the solution is accepted, it is added to solutions, i.e. the solutions-collections is modified.

Specified by:

acceptSolution in interface SolutionAcceptor

Parameters:

solutions - collection of existing solutions

newSolution - new solution to be evaluated

Returns:

true if solution accepted

acceptSolution

public boolean acceptSolution(VehicleRoutingProblemSolution solution,
                              VehicleRoutingProblemSolution newSolution)

toString

public String toString()

Overrides:

toString in class Object

getInitialThreshold

public double getInitialThreshold()

setInitialThreshold

public void setInitialThreshold(double initialThreshold)

Sets initial threshold.

Note that if initial threshold has been set, automatic generation of initial threshold is disabled.

Parameters:

initialThreshold - the initialThreshold to set

setMaxIterations

public void setMaxIterations(int maxIteration)

incIteration

public void incIteration()

informAlgorithmStarts

public void informAlgorithmStarts(VehicleRoutingProblem problem,
                                  VehicleRoutingAlgorithm algorithm,
                                  Collection<VehicleRoutingProblemSolution> solutions)

Specified by:

informAlgorithmStarts in interface AlgorithmStartsListener

informIterationStarts

public void informIterationStarts(int i,
                                  VehicleRoutingProblem problem,
                                  Collection<VehicleRoutingProblemSolution> solutions)

Specified by:

informIterationStarts in interface IterationStartsListener