org.cpsolver.exam.heuristics

Class ExamConstruction

java.lang.Object

org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext<Exam,ExamPlacement,ExamConstruction.Context>

org.cpsolver.exam.heuristics.ExamConstruction

All Implemented Interfaces:

CanHoldContext, HasAssignmentContext<Exam,ExamPlacement,ExamConstruction.Context>, NeighbourSelection<Exam,ExamPlacement>

public class ExamConstruction
extends NeighbourSelectionWithContext<Exam,ExamPlacement,ExamConstruction.Context>

Initial solution construction heuristics.

While there are exams that are still not assigned:

• The worst unassigned exam is selected (using Exam.compareTo(Exam))
• The best period that does not break any hard constraint and for which there is a room assignment available is selected together with the set the best available rooms for the exam in the best period (computed using Exam.findBestAvailableRooms(Assignment, ExamPeriodPlacement)).

If problem property ExamConstruction.CheckLocalOptimality is true, local (time) optimality is enforced at the end of this phase. During this procedure, for each exam, it tries to change the period of the exam so that the time cost is lower (see ExamPlacement.getTimeCost(Assignment)), but no hard constraint is violated. The problem is considered locally optimal if there is no such move.

Version:

ExamTT 1.3 (Examination Timetabling)
Copyright (C) 2008 - 2014 Tomáš Müller
muller@unitime.org
http://muller.unitime.org

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not see http://www.gnu.org/licenses/.

Author:

Tomáš Müller

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	ExamConstruction.Context

Field Summary

Fields inherited from class org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext

iContextOverride

Fields inherited from interface org.cpsolver.ifs.assignment.context.CanHoldContext

sMaxSize

Constructor Summary

Constructors

Constructor and Description
ExamConstruction(DataProperties properties) Constructor

Method Summary

Modifier and Type	Method and Description
Neighbour<Exam,ExamPlacement>	checkLocalOptimality(Assignment<Exam,ExamPlacement> assignment, ExamModel model) Find a new assignment of one of the assigned exams that improves the time cost ExamPlacement.getTimeCost(Assignment) and for which there is a set of available rooms Exam.findBestAvailableRooms(Assignment, ExamPeriodPlacement).
ExamConstruction.Context	createAssignmentContext(Assignment<Exam,ExamPlacement> assignment) Create a new assignment context for the given assignment.
void	init(Solver<Exam,ExamPlacement> solver) Initialization
Neighbour<Exam,ExamPlacement>	selectNeighbour(Solution<Exam,ExamPlacement> solution) Select a neighbour.

Methods inherited from class org.cpsolver.ifs.assignment.context.NeighbourSelectionWithContext

getAssignmentContextReference, getContext, getContext, hasContextOverride, isSingleContextSolver, setAssignmentContextReference

Methods inherited from class java.lang.Object

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

Constructor Detail

ExamConstruction

public ExamConstruction(DataProperties properties)

Constructor

Parameters:

properties - problem properties

Method Detail

init

public void init(Solver<Exam,ExamPlacement> solver)

Initialization

Specified by:

init in interface NeighbourSelection<Exam,ExamPlacement>

Overrides:

init in class NeighbourSelectionWithContext<Exam,ExamPlacement,ExamConstruction.Context>

Parameters:

solver - current solver

checkLocalOptimality

public Neighbour<Exam,ExamPlacement> checkLocalOptimality(Assignment<Exam,ExamPlacement> assignment,
                                                          ExamModel model)

Find a new assignment of one of the assigned exams that improves the time cost ExamPlacement.getTimeCost(Assignment) and for which there is a set of available rooms Exam.findBestAvailableRooms(Assignment, ExamPeriodPlacement). Return null, if there is no such assignment (the problem is considered locally optimal).

Parameters:

assignment - current assignment

model - problem model

Returns:

a neighbour to assign or null if none was found

selectNeighbour

public Neighbour<Exam,ExamPlacement> selectNeighbour(Solution<Exam,ExamPlacement> solution)

Select a neighbour. While there are exams that are still not assigned:

• The worst unassigned exam is selected (using Exam.compareTo(Exam))
• The best period that does not break any hard constraint and for which there is a room assignment available is selected together with the set the best available rooms for the exam in the best period (computed using Exam.findBestAvailableRooms(Assignment, ExamPeriodPlacement)).

Return null when done (all variables are assigned and the problem is locally optimal).

Parameters:

solution - given solution

Returns:

a neighbour assignment

createAssignmentContext

public ExamConstruction.Context createAssignmentContext(Assignment<Exam,ExamPlacement> assignment)

Description copied from interface: HasAssignmentContext

Create a new assignment context for the given assignment. If there are already some variables assigned in the value, the method should make sure that the context is appropriately initialized.

Parameters:

assignment - an assignment for which there needs to be an assignment context

Returns:

a new instance of the assignment context, filled according to the given assignment