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

InstanceClass 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

InstanceClass 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

InstanceClass get(VariantRef v1) const¶: Get the instance with the specified index.

InstanceClass get(VariantRef v1, VariantRef v2) const¶: Get the instance with the specified index.

InstanceClass get(VariantRef v1, VariantRef v2, VariantRef v3) const¶: Get the instance with the specified index.

InstanceClass 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

InstanceClass operator[](TupleRef index) const

InstanceClass operator[](VariantRef v1) const¶

Public Types

typedef internal::CountedIterator<internal::EntityWrapper<InstanceClass>> 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.

DataFrame getValues()

Get the principal values of this entity as a DataFrame. The specific returned value depends on the type of entity (see list below).

For:

Variables and Objectives it returns the suffix val
Parameters it returns their values
Constraints it returns the suffix dual
Sets it returns all the of the set. Note that it does not
apply to indexed sets. See SetInstance::getValues

Return: A DataFrame containing the values for all instances

DataFrame getValues(StringArgs suffixes)¶

Get the specified suffixes value for all instances in a DataFrame.

Return

A DataFrame containing the specified values

Parameters

suffixes: Suffixes to get

void setValues(DataFrame data)

Set the values of this entiy to the correponding values of a DataFrame indexed over the same sets (or a subset). This function assigns the values in the first data column of the passed dataframe to the entity the function is called from. In particular, the statement:

x.setValues(y.getValues());

is semantically equivalent to the AMPL statement:

let {s in S} x[s] := y[s];

Parameters

data: The data to set the entity to

StringArray getIndexingSets()

Get the AMPL string representation of the sets on which this entity is indexed.

The obtained vector can be modified without any effect to the entity.

Return: The string representation of the indexing sets for this entity or an empty array if the entity is scalar

std::string name(): Get the name of this entity.

std::size_t indexarity()

Get the indexarity of this entity (sum of the dimensions of the indexing sets).

This value indicates the arity of the Tuple to be passed to the method BasicEntity::get() in order to access an instance of this entity. See the following AMPL examples

var x;               # indexarity = 0
var y {1..2};        # indexarity = 1
var z {1..2,3..4};   # indexarity = 2
var zz {{(1, 2)}};   # indexarity = 2

Return: The sum of the dimensions of the indexing sets or 0 if the entity is not indexed

bool isScalar()

Check whether this entity is scalar.

Equivalent to testing whether indexarity() is equal to zero.

Return: True if the entity is scalar (not indexed over any set)

std::string toString(): Returns a string representation of this entity (its declaration)

std::size_t numInstances(): Get the number of instances in this entity.

enum ampl::var::Integrality¶

Integrality of variables.

See: Variable::integrality()

Values:

CONTINUOUS¶: Continuous variable.

BINARY¶: Binary variable.

INTEGER¶: Integer variable.

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