Parameter¶

class Parameter : public ampl::BasicEntity<VariantRef>¶

Represents an AMPL parameter.

The values can be Double or String (in case of symbolic parameters).

Data can be assigned to the parameter using the methods Parameter::set() and Parameter::setValues directly from objects of this class or using AMPL::setData and a DataFrame object.

Instance access

Methods to access the instances which are part of this Entity

VariantRef 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

VariantRef 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

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

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

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

VariantRef 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

VariantRef operator[](TupleRef index) const

VariantRef operator[](VariantRef v1) const¶

Public Types

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

Public Functions

bool isSymbolic() const¶: Returns true if the parameter is declared as symbolic (can store both numerical and string values)

bool hasDefault() const¶

Check if the parameter has a default initial value. In case of the following AMPL code:

param a;
param b default a;

the function will return true for parameter b.

Return: True if the parameter has a default initial value. Please note that if the parameter has a default expression which refers to another parameter which value is not defined, this will return true.

void setValues(const Tuple indices[], internal::Args values, std::size_t nvalues)¶

Assign the values (string or double) to the parameter instances with the specified indices, equivalent to the AMPL code:

let {i in indices} par[i] := values[i];

Parameters

indices: an array of indices of the instances to be set
values: values to set
nvalues: length of the values array

Exceptions

logic_error: If called on a scalar parameter

void setValues(std::size_t num_rows, internal::Args row_indices, std::size_t num_cols, internal::Args col_indices, const double *data, bool transpose)¶

Assign the specified values to a 2-d parameter, using the two dimensions as two indices.

For example, the \(m \times n\) matrix:

\[\begin{split}`A = \left( \begin{array}{cccc} a_{11} & a_{12} & ... & a_{1n} \\ a_{21} & a_{22} & ... & a_{2n} \\ ... & ... & ... & ... \\ a_{ m1} & a_{m2} & ... & a_{mn} \end{array} \right)`\end{split}\]

can be assigned to the AMPL parameter: param A {1..m, 1..n}; with the statement setValues(A, false).

As an example, to assign the matrix:

\[\begin{split}`A = \left( \begin{array}{cccc} 11 & 12 \\ 21 & 22 \\ 31 & 32 \end{array} \right)`\end{split}\]

to the AMPL paramater: param A{1..3, 1..2}; we can use the following code:

ampl.eval("param a{1..3, 1..2};");
Parameter a = ampl.getParameter("a");

double values[6];
double rows[3];
double cols[2];
for (int i = 0; i < 3; i++) {
  rows[i] = i + 1;
  for (int j = 0; j < 2; j++)
  values[i * 2 + j] = (i + 1) * 10 + (j + 1);
}
for (int i = 0; i < 2; i++)
  cols[i] = i + 1;

a.setValues(3, rows, 2, cols, values, false);

Parameters

num_rows: Number of rows
row_indices: Indices of the rows
num_cols: Number of rows
col_indices: Indices of the rows
data: Values to be assigned
transpose: True to transpose the values in the matrix

Exceptions

logic_error: If the method is called on a parameter which is not two-dimensional
invalid_argument: If the size of ‘values’ do not correspond to the sizes of the underlying indices

void setValues(internal::Args values, std::size_t n)¶

Assign the specified n values to this parameter, assigning them to the parameter in the same order as the indices in the entity.

The number of values in the array must be equal to the specified size.

Parameters

values: Values to be assigned.
n: Number of values to be assigned (must be equal to the number of instances in this parameter)

Exceptions

invalid_argument: If trying to assign a string to a non symbolic parameter
logic_error: If the number of arguments is not equal to the number of instances in this parameter

void set(VariantRef value)¶

Set the value of a scalar parameter.

Exceptions

runtime_error: if the entity has been deleted in the underlying AMPL
logic_error: if this parameter is not scalar.

void set(VariantRef index, VariantRef value)¶

Set the value of a single instance of this parameter.

Exceptions

runtime_error: if the entity has been deleted in the underlying AMPL

void set(TupleRef index, VariantRef value)¶

Set the value of a single instance of this parameter.

Exceptions

runtime_error: if the entity has been deleted in the underlying AMPL

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

iterator begin(): Get an iterator pointing to the first instance in this entity.

iterator end(): 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.

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.

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