# Entity¶

class Entity

An AMPL entity such as a parameter or a variable.

An entity can either represent a single instance of an AMPL algebraic entity or, if the corresponding declaration has an indexing expression, a mapping from keys to instances. In the derived classes, it has methods to access instance-level properties which can be used in case the represented entity is scalar.

To gain access to all the values in an entity (for all instances and all suffixes for that entities), use the function Entity::getValues().

The algebraic entities which currenty have an equivalent class in the API are:

Public Functions

std::string name() const

Get the name of this entity.

std::string type() const

Get the type of this entity.

std::size_t indexarity() const

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 Entity::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() const

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::size_t numInstances() const

Get the number of instances in this entity.

StringArray getIndexingSets() const

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

DataFrame getValues() const

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) const

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

std::string toString() const

Returns a string representation of this entity (its declaration)

template <class I>
Entity(BasicEntity<I> other)

Constructor to allow implicit conversion.

Entity &operator=(const Entity &rhs)

Assignment operator.

Entity()

Constructor to allow the construction of arrays of entities.

Friends

friend ampl::Entity::AMPL
friend ampl::Entity::DataFrame
friend ampl::Entity::EntityArgs
friend ampl::Entity::Instance
template <class InstanceClass>
class

Infrastructure class to enable the inheriting classes type-safe access to instances.

Subclassed by ampl::Constraint, ampl::Set

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 operator[](TupleRef index) const
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 operator[](VariantRef v1) const
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

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

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.

BasicEntity(internal::EntityBase *entity)

Constructor allowing cross conversions.

class EntityArgs

Represents a list of entities, to be passed as arguments to various API functions.

Public Functions

EntityArgs(Entity arg0)

Constructor from entities.

Parameters
• arg0: First entity

EntityArgs(Entity arg0, Entity arg1)

Constructor from entities.

Parameters
• arg0: First entity
• arg1: Second entity

EntityArgs(Entity arg0, Entity arg1, Entity arg2)

Constructor from entities.

Parameters
• arg0: First entity
• arg1: Second entity
• arg2: Third entity

EntityArgs(Entity arg0, Entity arg1, Entity arg2, Entity arg3)

Constructor from entities.

Parameters
• arg0: First entity
• arg1: Second entity
• arg2: Third entity
• arg3: Fourth entity

EntityArgs(const Entity args[], std::size_t size)

Constructor from an array of entities.

Parameters
• args: An array of entities
• size: Size of the array

const internal::EntityBase *const *getArgs() const

std::size_t size() const