Package org.tweetyproject.math.opt.problem

Class OptimizationProblem

java.lang.Object

java.util.AbstractCollection<OptProbElement>

java.util.AbstractSet<OptProbElement>

java.util.HashSet<OptProbElement>

org.tweetyproject.math.opt.problem.GeneralConstraintSatisfactionProblem

org.tweetyproject.math.opt.problem.ConstraintSatisfactionProblem

org.tweetyproject.math.opt.problem.OptimizationProblem

All Implemented Interfaces:

Serializable, Cloneable, Iterable<OptProbElement>, Collection<OptProbElement>, Set<OptProbElement>

public class OptimizationProblem
extends ConstraintSatisfactionProblem

This class models a general optimization problem.

Author:

Matthias Thimm

See Also:

• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
static final double	EPSILON	Some value to represent a very small number
static final int	MAXIMIZE	Static constant for the type "maximization"
static final int	MINIMIZE	Static constant for the type "minimization"

Constructor Summary

Constructors

Constructor	Description
OptimizationProblem()	Creates an empty optimization problem.
OptimizationProblem(int type)	Creates an empty optimization problem of the given type.

Method Summary

Modifier and Type	Method	Description
OptimizationProblem	clone()
void	collapseAssociativeOperations()	This method collapses all associative operations appearing in the target function and the constraints, e.g.
String	convertToCplexLpFormat()	Converts the this optimization problem into a string in the commonly used CPLEX LP-format for mixed integer linear programming.
String	convertToLpFormat()	Converts the this optimization problem into a string in the commonly used LP-format for mixed integer linear programming.
Set<Minimum>	getMinimums()	Returns all minimums appearing in this problem.
Term	getTargetFunction()	Returns the target function of this problem.
int	getType()	Returns the type of this problem.
Set<Variable>	getVariables()	Returns all variables of this problem.
boolean	isLinear()	Checks whether every constraint of this problem is linear.
boolean	isMinimumFree()	Checks whether this problem uses no minimum function.
boolean	isTargetLinear()	Checks whether the target function is linear.
void	resolveAbsoluteValues()	Resolves all occurrences of absolute values "abs(X)" by replacing "abs(X)" by a new variable "TMPABS" adding constraints "TMPABS - X>= 0" and "TMPABS + X >= 0" (yielding "TMPABS <= abs(X)") introducing a new variable "TMPABSB" adding constraints "X+PENALTY*TMPABSB - TMPABS >= 0" and "-X-TMPABSB*PENALTY - TMPABS >= -PENALTY" (yielding "TMPABS >= abs(X)") adding constraints "TMPABSB<=1"
void	resolveMaximums()	Resolves all occurrences of maximums by substituting a maximum "max{a,b}" by "0.5 a + 0.5 b + abs(a-b)".
void	resolveMinimums()	Resolves all occurrences of minimums by substituting a minimum "min{a,b}" by "0.5 a + 0.5 b - abs(a-b)".
void	setPenalty(int penalty)	Sets the penalty for violated minimum.
void	setTargetFunction(Term targetFunction)	Sets the target function of this problem.
void	setType(int type)	Sets the type of this problem, either OptimizationProblem.MINIMIZE or OptimizationProblem.MAXIMIZE.
String	toString()

Methods inherited from class org.tweetyproject.math.opt.problem.ConstraintSatisfactionProblem

isInteger, toNormalizedForm

Methods inherited from class java.util.HashSet

add, clear, contains, isEmpty, iterator, newHashSet, remove, size, spliterator, toArray, toArray

Methods inherited from class java.util.AbstractSet

equals, hashCode, removeAll

Methods inherited from class java.util.AbstractCollection

addAll, containsAll, retainAll

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

parallelStream, removeIf, stream, toArray

Methods inherited from interface java.lang.Iterable

forEach

Methods inherited from interface java.util.Set

addAll, containsAll, equals, hashCode, removeAll, retainAll

Field Details

EPSILON

public static final double EPSILON

Some value to represent a very small number

See Also:

• Constant Field Values

MINIMIZE

public static final int MINIMIZE

Static constant for the type "minimization"

See Also:

• Constant Field Values

MAXIMIZE

public static final int MAXIMIZE

Static constant for the type "maximization"

See Also:

• Constant Field Values

Constructor Details

OptimizationProblem

public OptimizationProblem()

Creates an empty optimization problem.

OptimizationProblem

public OptimizationProblem(int type)

Creates an empty optimization problem of the given type.

Parameters:

type - the type of the problem; either OptimizationProblem.MINIMIZE or OptimizationProblem.MAXIMIZE.

Method Details

setTargetFunction

public void setTargetFunction(Term targetFunction)

Sets the target function of this problem.

Parameters:

targetFunction - a term.

isTargetLinear

public boolean isTargetLinear()

Checks whether the target function is linear.

Returns:

"true" if the target function is linear.

isLinear

public boolean isLinear()

Description copied from class: ConstraintSatisfactionProblem

Checks whether every constraint of this problem is linear.

Overrides:

isLinear in class ConstraintSatisfactionProblem

Returns:

"true" if every constraint of this problem is linear.

isMinimumFree

public boolean isMinimumFree()

Description copied from class: ConstraintSatisfactionProblem

Checks whether this problem uses no minimum function.

Overrides:

isMinimumFree in class ConstraintSatisfactionProblem

Returns:

"true" if this problem uses no minimum function.

resolveMinimums

public void resolveMinimums()

Description copied from class: ConstraintSatisfactionProblem

Resolves all occurrences of minimums by substituting a minimum "min{a,b}" by "0.5 a + 0.5 b - abs(a-b)".

Overrides:

resolveMinimums in class ConstraintSatisfactionProblem

resolveMaximums

public void resolveMaximums()

Description copied from class: ConstraintSatisfactionProblem

Resolves all occurrences of maximums by substituting a maximum "max{a,b}" by "0.5 a + 0.5 b + abs(a-b)".

Overrides:

resolveMaximums in class ConstraintSatisfactionProblem

resolveAbsoluteValues

public void resolveAbsoluteValues()

Resolves all occurrences of absolute values "abs(X)" by

• replacing "abs(X)" by a new variable "TMPABS"
• adding constraints "TMPABS - X>= 0" and "TMPABS + X >= 0" (yielding "TMPABS <= abs(X)")
• introducing a new variable "TMPABSB"
• adding constraints "X+PENALTY*TMPABSB - TMPABS >= 0" and "-X-TMPABSB*PENALTY - TMPABS >= -PENALTY" (yielding "TMPABS >= abs(X)")
• adding constraints "TMPABSB<=1"

convertToLpFormat

public String convertToLpFormat()

Converts the this optimization problem into a string in the commonly used LP-format for mixed integer linear programming.

Returns:

A string representing this problem in LP-format

convertToCplexLpFormat

public String convertToCplexLpFormat()

Converts the this optimization problem into a string in the commonly used CPLEX LP-format for mixed integer linear programming.

Returns:

A string representing this problem in CPLEX LP-format

getVariables

public Set<Variable> getVariables()

Description copied from class: ConstraintSatisfactionProblem

Returns all variables of this problem.

Overrides:

getVariables in class ConstraintSatisfactionProblem

Returns:

all variables of this problem.

getMinimums

public Set<Minimum> getMinimums()

Description copied from class: ConstraintSatisfactionProblem

Returns all minimums appearing in this problem.

Overrides:

getMinimums in class ConstraintSatisfactionProblem

Returns:

all minimums appearing in this problem.

collapseAssociativeOperations

public void collapseAssociativeOperations()

Description copied from class: ConstraintSatisfactionProblem

This method collapses all associative operations appearing in the target function and the constraints, e.g. every min{min{a,b},c} becomes min{a,b,c}

Overrides:

collapseAssociativeOperations in class ConstraintSatisfactionProblem

setType

public void setType(int type)

Sets the type of this problem, either OptimizationProblem.MINIMIZE or OptimizationProblem.MAXIMIZE.

Parameters:

type - the type of this problem.

setPenalty

public void setPenalty(int penalty)

Sets the penalty for violated minimum.

Parameters:

penalty - some penalty

getType

public int getType()

Returns the type of this problem.

Returns:

the type of this problem.

getTargetFunction

public Term getTargetFunction()

Returns the target function of this problem.

Returns:

the target function of this problem.

toString

public String toString()

Overrides:

toString in class ConstraintSatisfactionProblem

clone

public OptimizationProblem clone()

Overrides:

clone in class ConstraintSatisfactionProblem