Class Presolvers

java.lang.Object

org.ojalgo.optimisation.Presolvers

public abstract class Presolvers
extends Object

Field Summary

Fields

Modifier and Type	Field	Description
static final ExpressionsBasedModel.Presolver	INTEGER
private static final NumberContext	LEVEL
static final ExpressionsBasedModel.Presolver	LINEAR_OBJECTIVE	If the expression is linear and contributes to the objective function, then the contributions are transferred to the variables and the weight of the expression set to null.
(package private) static final MathContext	LOWER
static final ExpressionsBasedModel.Presolver	REDUNDANT_CONSTRAINT	Calculates the min and max value of this expression based on the variables' individual bounds.
private static final MathContext	SIMILARITY
static final ExpressionsBasedModel.VariableAnalyser	UNREFERENCED	Verifies that the variable is actually referenced/used in some expression.
(package private) static final MathContext	UPPER
static final ExpressionsBasedModel.Presolver	ZERO_ONE_TWO	Looks for constraint expressions with 0, 1 or 2 non-fixed variables.

Constructor Summary

Constructors

Constructor	Description
Presolvers()

Method Summary

Modifier and Type	Method	Description
static void	checkFeasibility(Expression expression, Set<Structure1D.IntIndex> remaining, BigDecimal lower, BigDecimal upper, NumberContext precision, boolean relaxed)
static boolean	checkSimilarity(Collection<Expression> current, Expression potential)	Checks if the potential Expression is similar to any in the current collection.
(package private) static boolean	doCase0(Expression expression, Set<Structure1D.IntIndex> remaining, BigDecimal lower, BigDecimal upper, NumberContext precision)	This constraint expression has 0 remaining free variable.
(package private) static boolean	doCase1(Expression expression, Set<Structure1D.IntIndex> remaining, BigDecimal lower, BigDecimal upper, NumberContext precision)	This constraint expression has 1 remaining free variable.
(package private) static boolean	doCase2(Expression expression, Set<Structure1D.IntIndex> remaining, BigDecimal lower, BigDecimal upper, NumberContext precision)	Checks if bounds on either of the variables (together with the expressions's bounds) implies tighter bounds on the other variable.
(package private) static boolean	doCaseN(Expression expression, Set<Structure1D.IntIndex> remaining, BigDecimal lower, BigDecimal upper, NumberContext precision)	Checks the sign of the limits and the sign of the expression parameters to deduce variables that in fact can only be zero.
(package private) static BigDecimal	findCommonLevel(BigDecimal a, BigDecimal b)
static boolean	reduce(Collection<Expression> expressions)

Methods inherited from class Object

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

Field Details

INTEGER

public static final ExpressionsBasedModel.Presolver INTEGER

LINEAR_OBJECTIVE

public static final ExpressionsBasedModel.Presolver LINEAR_OBJECTIVE

If the expression is linear and contributes to the objective function, then the contributions are transferred to the variables and the weight of the expression set to null.

REDUNDANT_CONSTRAINT

public static final ExpressionsBasedModel.Presolver REDUNDANT_CONSTRAINT

Calculates the min and max value of this expression based on the variables' individual bounds. Then compares those with the expression's bounds.

UNREFERENCED

public static final ExpressionsBasedModel.VariableAnalyser UNREFERENCED

Verifies that the variable is actually referenced/used in some expression. If not then that variable can either be fixed or marked as unbounded.

2019-02-15: Turned this off. Very slow for large models
2019-02-22: Turned this on again, different implementation

ZERO_ONE_TWO

public static final ExpressionsBasedModel.Presolver ZERO_ONE_TWO

Looks for constraint expressions with 0, 1 or 2 non-fixed variables. Transfers the constraints of the expressions to the variables and then (if possible) marks the expression as redundant.

LEVEL

private static final NumberContext LEVEL

SIMILARITY

private static final MathContext SIMILARITY

LOWER

static final MathContext LOWER

UPPER

static final MathContext UPPER

Constructor Details

Presolvers

public Presolvers()

Method Details

checkFeasibility

public static void checkFeasibility(Expression expression,
 Set<Structure1D.IntIndex> remaining,
 BigDecimal lower,
 BigDecimal upper,
 NumberContext precision,
 boolean relaxed)

checkSimilarity

public static boolean checkSimilarity(Collection<Expression> current,
 Expression potential)

Checks if the potential Expression is similar to any in the current collection. Only works for linear expressions. If the potential expression to check has any quadratic term, nothing more is checked, and false is returned.

Returns:

true, if the potential Expression is found to be similar and marked as redundant by this method.

reduce

public static boolean reduce(Collection<Expression> expressions)

doCase0

static boolean doCase0(Expression expression,
 Set<Structure1D.IntIndex> remaining,
 BigDecimal lower,
 BigDecimal upper,
 NumberContext precision)

This constraint expression has 0 remaining free variable. It is entirely redundant.

doCase1

static boolean doCase1(Expression expression,
 Set<Structure1D.IntIndex> remaining,
 BigDecimal lower,
 BigDecimal upper,
 NumberContext precision)

This constraint expression has 1 remaining free variable. The lower/upper limits can be transferred to that variable, and the expression marked as redundant.

doCase2

static boolean doCase2(Expression expression,
 Set<Structure1D.IntIndex> remaining,
 BigDecimal lower,
 BigDecimal upper,
 NumberContext precision)

Checks if bounds on either of the variables (together with the expressions's bounds) implies tighter bounds on the other variable.

doCaseN

static boolean doCaseN(Expression expression,
 Set<Structure1D.IntIndex> remaining,
 BigDecimal lower,
 BigDecimal upper,
 NumberContext precision)

Checks the sign of the limits and the sign of the expression parameters to deduce variables that in fact can only be zero.

findCommonLevel

static BigDecimal findCommonLevel(BigDecimal a,
 BigDecimal b)