ConstraintInstance

public class ConstraintInstance extends Instance<Constraint>

This class represent an instance of a constraint.

In general, all AMPL suffixes for a constraint are available through methods with the same name in this class. See http://www.ampl.com/NEW/suffbuiltin.html for a list of the available suffixes.

Note that, since this class represents instances of both algebraic and logical constraints, some suffixes might not be available for every instance. If a wrong suffix for the specific class of constraint is accessed, an UnsupportedOperationException is thrown.

All the accessors in this class throw a IllegalStateException if the instance has been deleted in the underlying AMPL interpreter.

Methods

public String astatus()

Get the current AMPL status (dropped, presolved, or substituted out)

public double body()

Body of the constraint

Returns:Value

public int defvar()

Get the index in _var of “defined variable” substituted out by the constraint

public double dinit()

Get the current initial guess for the constraint’s dual variable

public double dinit0()

Get the original initial guess for the constraint’s dual variable

public void drop()

Drop this constraint instance

public double dual()

Get the current value of the constraint’s dual variable.

Note that dual values are often reset by the underlying AMPL interpreter by the presolve functionalities triggered by some methods. A possible workaround is to set the option presolve to false (see AMPL.setBoolOption).

public double lb()

Get the current value of the constraint’s lower bound

public double lbs()

Get the constraint lower bound sent to the solver (reflecting adjustment for fixed variables)

public double ldual()

Get the current dual value associated with the lower bound

public double lslack()

Get the slack at lower bound body - lb

public void restore()

Restore this constraint instance (if it had been dropped, no effect otherwise)

public void setDual(double dual)

Set the value of the dual variable associated to this constraint.

Equivalent to the AMPL statement:

let c := dual;

Note that dual values are often reset by the underlying AMPL interpreter by the presolve functionalities triggered by some methods. A possible workaround is to set the option presolve to false (see AMPL.setBoolOption).

Parameters:

• dual – The value to be assigned to the dual variable

public double slack()

Constraint slack (the lesser of lslack and uslack)

public String sstatus()

Get the solver status (basis status of constraint’s slack or artificial variable)

public String status()

Get the AMPL status if not in otherwise solver status

public String toString()

Returns a string representation of this instance. Returns the equivalent to the AMPL statement:

expand instanceName;

public double ub()

Get the current value of the constraint’s upper bound

public double ubs()

Get the constraint upper bound sent to the solver (reflecting adjustment for fixed variables)

public double udual()

Get the current dual value associated with the upper bounds

public double uslack()

Get the slack at upper bound ub - body

public double val()

Get the AMPL val suffix. Valid only for logical constraints.