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94 lines
4.8 KiB
Markdown
94 lines
4.8 KiB
Markdown
It is assumed that you know the basics of the [applied algorithm](Meta-Heuristic.md). In the recreation-step each
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removed job is re-inserted into the ruined solution again (one after another). To actually insert a job, the algorithm
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calculates its "best" insertion position. This implies also to check the feasibility of the insertion step
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which is in turn dependent on constraints (such as capacity constraints).
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## jsprit knows hard and soft constraints.
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- Hard constraints must be met and cannot be broken
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- soft constraints are always fulfilled but uses penalties to express "good" and "bad" insertions.
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jsprit comes with built-in or default constraints (such as capacity and time-window constraints) and allows you to add
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custom constraints. However, you can also disable the default constraints. To add custom constraints use
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<code>core.algorithm.VehicleRoutingAlgorithmBuilder</code> to build an algorithm instead of
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<code>core.algorithm.io.VehicleRoutingAlgorithms</code>.
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Note that
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<pre><code>VehicleRoutingAlgorithmBuilder vraBuilder = new VehicleRoutingAlgorithmBuilder(routingProblem, "yourAlgorithmConfig");
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vraBuilder.addCoreConstraints();
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vraBuilder.addDefaultCostCalculators();
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VehicleRoutingAlgorithm vra = vraBuilder.build();
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</code></pre>
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is equivalent to
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<pre><code>VehicleRoutingAlgorithm vra = VehicleRoutingAlgorithms.readAndCreateAlgorithm(routingProblem, "yourAlgorithmConfig");;
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</code></pre>
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To add custom constraints add the following lines:
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<pre><code>VehicleRoutingAlgorithmBuilder vraBuilder = new VehicleRoutingAlgorithmBuilder(routingProblem, "yourAlgorithmConfig");
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vraBuilder.addCoreConstraints();
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vraBuilder.addDefaultCostCalculators();
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//add custom constraint
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StateManager stateManager = new StateManager(routingProblem.getTransportCosts());
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ConstraintManager constraintManager = new ConstraintManager(routingProblem, stateManager);
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constraintManager.addConstraint(customConstraint);
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vraBuilder.setStateAndConstraintManager(stateManager, constraintManager);
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VehicleRoutingAlgorithm vra = vraBuilder.build();
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</code></pre>
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## Hard constraints
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There are hard constraints at two different levels: at route and activity level.
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A route is basically a sequence of activities. Each route has a start- and an end-activity, and in between other activities of type <code>core.problem.solution.route.activity.TourActivity</code>.
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### <code>core.problem.constraint.HardRouteConstraint</code>
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A HardRouteConstraint indicates whether a specified job can be inserted into an existing route (along with a specified vehicle). To define it you need to implement the HardRouteConstraint-interface:
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<pre><code>HardRouteConstraint constraint = new HardRouteConstraint(){
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@Override
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public boolean fulfilled(JobInsertionContext iContext) {
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return true;
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};
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};
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</code></pre>
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The JobInsertionContext tells you the context of the insertion step, i.e. the specified job (<code>iContext.getJob()</code>) to be inserted into
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a specified route (<code>iContext.getRoute()</code>) as well as the vehicle
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that should be employed on that route (<code>iContext.getNewVehicle()</code>).
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#### Example:
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Assume a vehicle with id="1" is not allowed to serve a job with id="job1" (since it is for example too big to access the customer location). Such a constraint can be easily defined as follows:
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<pre><code>final Job jobWithAccessConstraint = routingProblem.getJobs().get("job1");
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HardRouteConstraint accessConstraint = new HardRouteConstraint() {
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@Override
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public boolean fulfilled(JobInsertionContext iContext) {
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if(iContext.getNewVehicle().getId().equals("1")){
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if(iContext.getJob()==jobWithAccessConstraint || iContext.getRoute().getTourActivities().servesJob(jobWithAccessConstraint)){
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return false;
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}
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}
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return true;
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}
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};
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constraintManager.addConstraint(accessConstraint);
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</code></pre>
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<strong>Note</strong> that if vehicleSwitches are not allowed, you are done with the first term <code>iContext.getJob()==jobWithAccessConstraint</code> in the above if-clause. If they are, you need to add the second term <code>iContext.getRoute().getTourActivities().servesJob(jobWithAccessConstraint</code> as well to prohibit the vehicle (id=1) to take over a route that already contains job1.
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### core.problem.constraint.HardActivityConstraint
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to be documented ... (as long as it is not yet documented it might be helpful to see how the [service backhaul constraint](https://github.com/jsprit/jsprit/blob/master/jsprit-core/src/main/java/jsprit/core/problem/constraint/ServiceDeliveriesFirstConstraint.java) is implemented which you can add to the constraintManager much like the above access constraint)
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## Soft constraints
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to be documented ... (as long as it is not yet documented the following examples might be helpful http://stackoverflow.com/questions/24447451/related-jobs-in-jsprit)
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