Variable

class Variable : public ampl::BasicEntity<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 std::logic_error if called for an entity which is not scalar and an std::runtime_error if the entity has been deleted.

The instances, represented by the class VariableInstance can be accessed via the operator Variable::operator[](), via the methods Variable::get() or via the iterators provided.

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.

Instance access

Methods to access the instances which are part of this Entity

VariableInstance get() const

Get the instance corresponding to a scalar entity.

Return

The corresponding instance.

Exceptions

• runtime_error: if the entity has been deleted in the underlying AMPL interpreter
• logic_error: if the entity is not scalar

VariableInstance get(TupleRef index) const

Get the instance with the specified index.

Return

The corresponding instance

Parameters

• index: The tuple specifying the index

Exceptions

• out_of_range: if an instance with the specified index does not exist
• out_of_range: if the entity has been deleted in the underlying AMPL interpreter
• ampl::UnsupportedOperationException: if the entity is scalar

VariableInstance get(VariantRef v1) const

Get the instance with the specified index.

VariableInstance get(VariantRef v1, VariantRef v2) const

Get the instance with the specified index.

VariableInstance get(VariantRef v1, VariantRef v2, VariantRef v3) const

Get the instance with the specified index.

VariableInstance get(VariantRef v1, VariantRef v2, VariantRef v3, VariantRef v4) const

Get the instance with the specified index.

Return

The corresponding instance

Parameters

• v1: The VariantRef specifying the first element of the indexing tuple
• v2: The VariantRef specifying the second element of the indexing tuple
• v3: The VariantRef specifying the third element of the indexing tuple
• v4: The VariantRef specifying the fourth element of the indexing tuple

Exceptions

• out_of_range: if an instance with the specified index does not exist
• runtime_error: if the entity has been deleted in the underlying AMPL interpreter
• ampl::UnsupportedOperationException: if the entity is scalar

VariableInstance operator[](TupleRef index) const

VariableInstance operator[](VariantRef v1) const

Public Types

typedef internal::CountedIterator<internal::EntityWrapper<VariableInstance>> iterator

Iterator for entities, represented by an iterator pointing to elements of type std::pair<TupleRef, InstanceClass>

Public Functions

double value() const

Get the current value of this variable.

var::Integrality integrality() const

Get the integrality type for this variable.

Return

Type of integrality (integer, binary, continuous)

void fix()

Fix all instances of this variable to their current value.

void fix(double value)

Fix all instances of this variable to the specified value.

void unfix()

Unfix this variable instances.

void setValue(double value)

Set the current value of this variable (does not fix it), equivalent to the AMPL command let

Parameters

• value: Value to be set

std::string astatus() const

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

int defeqn() const

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

double dual() const

Get the dual value on defining constraint of variable substituted out.

double init() const

Get the current initial guess.

double init0() const

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

double lb() const

Returns the current lower bound. See Note on variables suffixes.

double ub() const

Returns the current lower bound. See Note on variables suffixes.

double lb0() const

Returns the initial lower bounds, from the var declaration.

double ub0() const

Returns the initial upper bound, from the var declaration.

double lb1() const

Returns the weaker lower bound from AMPL’s presolve phase.

double ub1() const

Returns the weaker upper bound from AMPL’s presolve phase.

double lb2() const

Returns the stronger lower bound from AMPL’s presolve phase.

double ub2() const

Returns the stronger upper bound from AMPL’s presolve phase.

double lrc() const

Returns the reduced cost at lower bound.

double urc() const

Returns the reduced cost at upper bound.

double lslack() const

Return the slack at lower bound (val - lb). See Note on variables suffixes.

double uslack() const

Return the slack at upper bound (ub - val). See Note on variables suffixes.

double rc() const

Get the reduced cost (at the nearer bound)

double slack() const

Returns the bound slack which is the lesser of lslack() and uslack(). See Note on variables suffixes.

std::string sstatus() const

Solver status (basis status of variable)

std::string status() const

AMPL status if not in, otherwise solver status

iterator begin() const

Get an iterator pointing to the first instance in this entity.

iterator end() const

Get an iterator pointing after the last instance in this entity.

iterator find(TupleRef t) const

Searches the current entity for an instance with the specified index.

Return

an iterator to the wanted entity if found, otherwise an iterator to BasicEntity::end.

enum ampl::var::Integrality

Integrality of variables.

See

Variable::integrality()

Values:

CONTINUOUS

Continuous variable.

BINARY

Binary variable.

INTEGER

Integer variable.