Set
Declaration and Attributes
Set attributes
Each set has an optional list of attributes which further specify its
intended behavior in the model. The attributes of sets are given in
this table. The attributes IndexDomain
is only
relevant to indexed sets.
Attribute 
Valuetype 
See also 


indexdomain 


subsetdomain 


identifierlist 


identifierlist 


string 


comment string 





setexpression 


expressionlist 
Simple Sets
Definition
A simple set in AIMMS is a finite collection of elements. These elements are either strings or integers. Strings are typically used to identify realworld objects such as products, locations, persons, etc. Integers are typically used for algorithmic purposes. With every simple set you can associate indices through which you can refer (in succession) to all individual elements of that set in indexed statements and expressions.
Most basic example
An example of the most basic declaration for the set Cities from the previous example follows.
Set Cities {
Index : i,j;
}
This declares the identifier Cities
as a simple set, and binds the
identifiers i
and j
as indices to Cities
throughout your
model text.
More detailed example
Consider a set SupplyCities which is declared as follows:
Set SupplyCities {
SubsetOf : Cities;
Parameter : LargestSupplyCity;
Text : The subset of cities that act as supply city;
Definition : {
{ i  Exists( j  Transport(i,j) ) }
}
OrderBy : i;
}
The 
operator used in the definition is to be read as “such that”
(it is explained in Set, Set Element and String Expressions). Thus, SupplyCities
is
defined as the set of all cities from which there is transport to at
least one other city. All elements in the set are ordered
lexicographically. The set has no index of its own, but does have an
element parameter LargestSupplyCity
that can hold any particular
element with a specific property. For instance, the following assignment
forms one way to specify the value of this element parameter:
LargestSupplyCity := ArgMax( i in SupplyCities, sum( j, Transport(i,j) ) );
Note that this assignment selects that particular element from the
subset of SupplyCities
for which the total amount of Transport
leaving that element is the largest.
The SubsetOf
attribute
With the SubsetOf
attribute you can tell AIMMS that the set at hand
is a subset of another set, called the subset domain. For simple sets,
such a subset domain is denoted by a single set identifier. During the
execution of the model AIMMS will assert that this subset relationship
is satisfied at all times.
Root sets
Each simple set that is not a subset of another set is called a root set. As will be explained later on, root sets have a special role in AIMMS with respect to data storage and ordering.
The Index
attribute
An index takes the value of all elements of a set successively and in
the order specified by its declaration. It is used in operations like
summation and indexed assignment over the elements of a set. With the
Index
attribute you can associate identifiers as indices into the
set at hand. The index attributes of all sets must be unique
identifiers, i.e. every index can be declared only once.
The Parameter
attribute
A parameter declared in the Parameter
attribute of a set takes the
value of a specific element of that set. Throughout the sequel we will
refer to such a parameter as an element parameter. It is a very useful
device for referring to set elements that have a special meaning in your
model (as illustrated in the previous example). In a later chapter you
will see that an element parameter can also be defined separately as a
parameter which has a set as its range.
The Text
and Comment
attributes
With the Text
attribute you can specify one line of descriptive text
for the enduser. This description can be made visible in the graphical
user interface when the data of an identifier is displayed in a page
object. You can use the Comment
attribute to provide a longer
description of the identifier at hand. This description is intended for
the modeler and cannot be made visible to an enduser. The Comment
attribute is a multiline string attribute.
Quoting identifier names in Comment
You can make AIMMS aware that specific words in your comment text are intended as identifier names by putting them in single quotes. This has the advantage that AIMMS will update your comment when you change the name of that identifier in the model editor, or, that AIMMS will warn you when a quoted name does not refer to an existing identifier.
The OrderBy
attribute
With the OrderBy
attribute you can indicate that you want the
elements of a certain set to be ordered according to a single or
multiple ordering criteria. Only simple sets can be ordered.
Ordering root sets
A special word of caution is in place with respect to specifying an
ordering principle for root sets. Root sets play a special role within
AIMMS because all data defined over a root set or any of its subsets is
stored in the original data entry order in which elements have been
added to that root set. Thus, the data entry order defines the natural
order of execution over a particular domain, and specifying the
OrderBy
attribute of a root set may influence overall execution
times of your model in a negative manner. Set Element Ordering
discusses these efficiency aspects in more detail, and provides
alternative solutions.
Ordering criteria
The value of the OrderBy
attribute can be a commaseparated list of
one or more ordering criteria. The following ordering criteria (numeric,
string or userdefined) can be specified.
If the value of the
OrderBy
attribute is an indexed numerical expression defined over the elements of the set, AIMMS will order its elements in increasing order according to the numerical values of the expression.If the value of the
OrderBy
attribute is either an index into the set, a set elementvalued expression, or a string expression over the set, then its elements will be ordered lexicographically with respect to the strings associated with the expression. By preceding the expression with a minus sign, the elements will be ordered reverse lexicographically.If the value of the
OrderBy
attribute is the keywordUser
, the elements will be ordered according to the order in which they have been added to the subset, either by the user, the model, or by means of theSort
operator.
Specifying multiple criteria
When applying a single ordering criterion, the resulting ordering may not be unique. For instance, when you order according to the size of transport taking place from a city, there may be multiple cities with equal transport. You may want these cities to be ordered too. In this case, you can enforce a more refined ordering principle by specifying multiple criteria. AIMMS applies all criteria in succession, and will order only those elements that could not be uniquely distinguished by previous criteria.
Example
The following set declarations give examples of various types of automatic ordering. In the last declaration, the cities with equal transport are placed in a lexicographical order.
Set LexicographicSupplyCities {
SubsetOf : SupplyCities;
OrderBy : i;
}
Set ReverseLexicographicSupplyCities {
SubsetOf : SupplyCities;
OrderBy :  i;
}
Set SupplyCitiesByIncreasingTransport {
SubsetOf : SupplyCities;
OrderBy : sum( j, Transport(i,j) );
}
Set SupplyCitiesByDecreasingTransportThenLexicographic {
SubsetOf : SupplyCities;
OrderBy :  sum( j, Transport(i,j) ), i;
}
The Property
attribute
In general, you can use the Property
attribute to assign additional
properties to an identifier in your model. The applicable properties
depend on the identifier type. Sets, at the moment, only support a
single property.
The property
NoSave
specifies that the contents of the set at hand will never be stored in a case file. This can be useful, for instance, for intermediate sets that are necessary during the model’s computation, but are never important to an enduser.The properties
ElementsAreNumerical
andElementsAreLabels
are only relevant for integer sets (see also Integer Sets). They will ignored for noninteger sets.
Dynamic property selection
The properties selected in the Property
attribute of an identifier
are on
by default, while the nonselected properties are off
by
default. During execution of your model you can also dynamically change
a property setting through the Property
statement. The PROPERTY
statement is discussed in The OPTION and PROPERTY Statements.
The Definition
attribute
If an identifier can be uniquely defined throughout your model by a
single expression, you can (and should) use the Definition
attribute
to specify this global relationship. AIMMS stores the result of a
Definition
and recomputes it only when necessary. For sets where a
global Definition
is not possible, you can make assignments in
procedures and functions. The value of the Definition
attribute must
be a valid expression of the appropriate type, as exemplified in the
declaration
Set SupplyCities {
SubsetOf : Cities;
Definition : {
{ i  Exists( j  Transport(i,j) ) }
}
}
Integer Sets
Integer sets
A special type of simple set is an integer set. Such a set is
characterized by the fact that the value of the SubsetOf
attribute
must be equal to the predefined set Integers
or a subset thereof.
Integer sets are most often used for algorithmic purposes.
Usage in expressions
Elements of integer sets can also be used as integer values in numerical
expressions. In addition, the result of an integervalued expression can
be added as an element to an integer set. Elements of noninteger sets
that represent numerical values cannot be used directly in numerical
expressions. To obtain the numerical value of such noninteger elements,
you can use the Val
function (see
Intrinsic Functions for Sets and Set Elements).
Interpret values as integer or label?
The interpretation of integer set elements will as integer values in
numerical expressions, raises an ambiguity for certain types of
expressions. If anInteger
is an element parameter into an integer
set anIntegerSet
,
how should AIMMS handle the expression
if (anInteger) then ... endif;
where
anInteger
holds the value'0'
. On the one hand, it is not the empty element, so if AIMMS would interpret this as a logical expression with a nonempty element parameter, theif
statement would evaluate to true. If AIMMS would interpret this as a numerical expression, the element parameter would evaluate to the numerical value 0, and theif
statement would evaluate to false.how should AIMMS handle the assignment
anInteger := anInteger + 3;
if the values in
anIntegerSet
are noncontiguous? If AIMMS would interpretanInteger
as an ordinary element parameter, the+
operator would refer to a lead operator (see also Lag and Lead Element Operators), and the assignment would assign the third next element ofanInteger
in the setanIntegerSet
. If AIMMS would interpretanInteger
as an numerical value, the assignment would assign the numerical value ofanInteger
plus 3, assuming that this is an element ofanIntegerSet
.
You can resolve this ambiguity assigning one of the properties
ElementsAreLabels
and ElementsAreNumerical
to anIntegerSet
.
If you don’t assign either property, and you use one of these
expressions in your model, AIMMS will issue a warning about the
ambiguity, and the end result might be unpredictable.
Construction
In order to fill an integer set AIMMS provides the special operator
..
to specify an entire range of integer elements. This powerful
feature is discussed in more detail in Enumerated Sets.
Example
The following somewhat abstract example demonstrates some of the features of integer sets. Consider the following declarations.
Parameter LowInt {
Range : Integer;
}
Parameter HighInt {
Range : Integer;
}
Set EvenNumbers {
SubsetOf : Integers;
Index : i;
Parameter : LargestPolynomialValue;
OrderBy :  i;
}
The following statements illustrate some of the possibilities to compute integer sets on the basis of integer expressions, or to use the elements of an integer set in expressions.
! Fill the integer set with the even numbers between
! LowInt and HighInt. The first term in the expression
! ensures that the first integer is even.
EvenNumbers := { (LowInt + mod(LowInt,2)) .. HighInt by 2 };
! Next the square of each element i of EvenNumbers is added
! to the set, if not already part of it (i.e. the union results)
for ( i  i <= HighInt ) do
EvenNumbers += i^2;
endfor;
! Finally, compute that element of the set EvenNumbers, for
! which the polynomial expression assumes the maximum value.
LargestPolynomialValue := ArgMax( i, i^4  10*i^3 + 10*i^2  100*i );
Ordering integer sets
By default, integer sets are ordered according to the numeric value of
their elements. Like with ordinary simple sets, you can override this
default ordering by using the OrderBy
attribute. When you use an
index in specifying the order of an integer set, AIMMS will interpret it
as a numeric expression.
Relations
Relation
A relation or multidimensional set is the Cartesian product of a number of simple sets or a subset thereof. Relations are typically used as the domain space for multidimensional identifiers. Unlike simple sets, the elements of a relation cannot be referenced using a single index.
Tuples and index components
An element of a relation is called a tuple and is denoted by the usual mathematical notation, i.e. as a parenthesized list of commaseparated elements. Throughout, the word index component will be used to denote the index of a particular position inside a tuple.
Index tuple
To reference an element in a relation, you can use an index tuple, in which each tuple component contains an index corresponding to a simple set.
The SubsetOf
attribute
The SubsetOf
attribute is mandatory for relations, and must contain
the subset domain of the set. This subset domain is denoted either as
a parenthesized commaseparated list of simple set identifiers, or, if
it is a subset of another relation, just the name of that set.
Example
The following example demonstrates some elementary declarations of a
relation, given the twodimensional parameters Distance(i,j)
and
TransportCost(i,j)
. The following set declaration defines a
relation.
Set HighCostConnections {
SubsetOf : (Cities, Cities);
Definition : {
{ (i,j)  Distance(i,j) > 0 and TransportCost(i,j) > 100 }
}
}
Indexed Sets
Definition
An indexed set represents a family of sets defined for all elements in another set, called the index domain. The elements of all members of the family must be from a single (sub)set. Although membership tables allow you to reach the same effect, indexed sets often make it possible to express certain operations very concisely and intuitively.
The IndexDomain
attribute
A set becomes an indexed set by specifying a value for the
IndexDomain
attribute. The value of this attribute must be a single
index or a tuple of indices, optionally followed by a logical condition.
The precise syntax of the IndexDomain
attribute is discussed on
The IndexDomain attribute.
Example
The following declarations illustrate some indexed sets with a content that varies for all elements in their respective index domains.
Set SupplyCitiesToDestination {
IndexDomain : j;
SubsetOf : Cities;
Definition : {
{ i  Transport(i,j) }
}
}
Set DestinationCitiesFromSupply {
IndexDomain : i;
SubsetOf : Cities;
Definition : {
{ j  Transport(i,j) }
}
}
Set IntermediateTransportCities {
IndexDomain : (i,j);
SubsetOf : Cities;
Definition : DestinationCitiesFromSupply(i) * SupplyCitiesToDestination(j);
Comment : {
All intermediate cities via which an indirect transport
from city i to city j with one intermediate city takes place
}
The first two declarations both define a onedimensional family of
subsets of Cities
, while the third declaration defines a
twodimensional family of subsets of Cities
. Note that the *
operator is applied to sets, and therefore denotes intersection.
Subset domains
The subset domain of an indexed set family can be either a simple set identifier, or another family of indexed simple sets of the same or lower dimension. The subset domain of an indexed set cannot be a relation.
No default indices
Declarations of indexed sets do not allow you to specify either the
Index
or Parameter
attribute. Consequently, if you want to use
an indexed set for indexing, you must locally bind an index to it. For
more details on the use of indices and index binding refer to
INDEX Declaration and Attributes and Binding Rules.