Text Data Files

Allowed text formats

Text data files must contain one or a sequence of identifier assignments with a constant right-hand side. All assignments must be terminated by a semi-colon. The following constant formats can be assigned:

  • assignment of scalar constants,

  • assignment of constant enumerated set expressions,

  • assignment of constant enumerated list expressions,

  • assignment of constant tabular expressions, and

  • assignment via composite tables.

The first three formats can also be used in ordinary expressions, and have been discussed in Set, Set Element and String Expressions and Numerical and Logical Expressions. The tabular and composite table formats are mostly placed in external data files, and will be discussed in this chapter.

AIMMS generated output

When you use the WRITE statement to write the contents of some or all identifiers in your model to a text file, AIMMS will select the appropriate format and write the resulting output accordingly. If you want actual control over the way identifiers are printed, you should use the PUT or DISPLAY statements (see also The PUT Statement and The DISPLAY Statement).

Easily generated

The text formats allowed in AIMMS are straightforward, and it is not difficult to generate these formats either manually or through an external program. As a result, text files form an ideal input medium when you quickly need to create a small data set to test your AIMMS application, or when data is obtained from a program to which a direct link cannot be made.


The following initialization statements illustrate an arrangement of assignments of scalar constants, constant enumerated sets and lists which can be used in an text data file.

Cities      := DATA { Amsterdam, Rotterdam, Antwerp, Berlin, Paris } ;

Supply(i)   := DATA { Amsterdam :  50,
                      Rotterdam : 100,
                      Antwerp   :  75  } ;
PricePerMile := 50 ;

LargestCity := 'Paris' ;

Dimensions must match

There is an important rule that applies to any data initialization statement in an text data file: the dimensions of left-hand side identifier and the right-hand side expressions must be equal. For instance, the assignment

Supply(i) := 100 ;

cannot be made inside an text data file for data initialization. Of course, the above statement is a valid assignment when used inside a procedure in AIMMS.

Reducing the dimension

Sometimes it is more convenient to initialize multidimensional parameters and variables using several tables of lesser dimension than by providing a huge table covering the full index space at once. This is especially convenient when data in your model is supplied in natural portions (for instance, all city-dependent data separate for each city). AIMMS helps you in these situations by allowing you to initialize a slice of a parameter or a variable.

Sliced initialization

You can specify a slice of a non-scalar identifier by replacing one or more of its indices by explicit elements. The result of a slice can be either a scalar quantity which you can initialize by assigning a scalar, or a non-scalar quantity which you can initialize using either a enumerated list, a table, or a composite table.


The following data assignments illustrate valid examples of sliced initialization.

Supply('Amsterdam')     := 75;

Distance('Amsterdam',j) := DATA { Rotterdam :  85,
                                  Antwerp   : 170,
                                  Berlin    : 660,
                                  Paris     : 530  } ;