Variable

public class Variable extends Entity<VariableInstance>

Represents an AMPL decision variable. Note that, in case of a scalar variable, all the properties of the variable instance can be accessed through methods like Variable.value. The methods have the same name of the corresponding AMPL suffixes. See http://www.ampl.com/NEW/suffbuiltin.html for a list of the available suffixes.

All these methods throw an UnsupportedOperationException if called for an entity which is not scalar.

Otherwise, use the method Variable.get to obtain the objects of type VariableInstance, from which to access all properties (corresponding to AMPL suffixes). See section Access to instances and values for further information on how to access set instances.

To gain access to all the values in an entity (for all instances and all suffixes for that entities), see Entity.getValues and the DataFrame class.

Methods

public String astatus()

Get the AMPL status (fixed, presolved, or substituted out)

public int defeqn()

Get the index in _con of “defining constraint” used to substitute variable out

public double dual()

Get the dual value on defining constraint of variable substituted out

public void fix()

Fix all instances of this variable to their current value, equivalent to:

fix varname;

public void fix(double value)

(for scalar variables) fix the variable to the specified value, equivalent to:

fix varname := value;

public VariableInstance get()

Get the corresponding VariableInstance instance (for not indexed variables)

Throws:

• UnsupportedOperationException – if the entity is not scalar.
• IllegalStateException – if the entity has been deleted in the underlying AMPL

public final VariableInstance get(Object... key)

Get the variable instance corresponding to the specified key. See Access to instances and values for further information on how the key can be specified.

Parameters:

• key – The key to be found

Throws:

• IllegalArgumentException – if trying to access an instance with the wrong number of keys (see Entity.indexarity)
• IllegalStateException – if the entity has been deleted in the underlying AMPL interpreter

Returns:

The instance corresponding to the specified key. Returns null if the specified key is not present.

public VariableInstance get(Tuple key)

Get the variable instance corresponding to the specified key, expressed as a Tuple. See Access to instances and values for further information on how the key can be specified.

Parameters:

• key – The indexing Tuple of the instance to be found

Throws:

• IllegalArgumentException – if trying to access an instance with the wrong indexarity (see Entity.indexarity)
• IllegalStateException – if the entity has been deleted in the underlying AMPL interpreter

Returns:

The variable instance corresponding to the specified key. Returns null if the specified key is not present.

public double init()

Get the current initial guess

public double init0()

Get the original initial guess (set by := or default or by a data statement)

public Integrality integrality()

Get the integrality status

Returns:Type of integrality (integer, binary, continuous)

public double lb()

Returns the current lower bound

public double lb0()

Returns the initial lower bounds, from the var declaration

public double lb1()

Returns the weaker lower bound from AMPL’s presolve phase

public double lb2()

Returns the stronger lower bound from AMPL’s presolve phase

public double lrc()

Returns the reduced cost at lower bound

public double lslack()

Return the slack at lower bound (val - lb)

public double rc()

Get the reduced cost (at the nearer bound)

public void setValue(double value)

Set the current value of this variable instance

Parameters:

• value – Value to be set

Throws:

• UnsupportedOperationException – if the entity is not scalar

public double slack()

Returns the bound slack which is the lesser of lslack and uslack.

public String sstatus()

Solver status (basis status of variable)

public String status()

AMPL status if not in, otherwise solver status

public String toString()

Returns a string representation of this variable. Equivalent to the AMPL statement

show variableName;

public double ub()

Returns the current upper bound.

public double ub0()

Returns the initial upper bound, from the var declaration

public double ub1()

Returns the weaker upper bound from AMPL’s presolve phase

public double ub2()

Returns the stronger upper bound from AMPL’s presolve phase

public void unfix()

Unfix all instances of the current variable, equivalent to the AMPL code:

unfix varname;

public double urc()

Returns the reduced cost at upper bound

public double uslack()

Return the slack at upper bound (ub - val)

public double value()

Get the current value of this variable instance