GAMS Tutorial

8 A GAMS Tutorial by Richard E. Rosenthal
Inputs:
• Sets
Declaration
Assignment of members
• Data (Parameters, Tables, Scalars)
Declaration
Assignment of values
• Variables
Declaration
Assignment of type
• Assignment of bounds and/or initial values (optional)
• Equations
Declaration
Definition
• Model and Solve statements
• Display statement (optional)
Outputs:
• Echo Print
• Reference Maps
• Equation Listings
• Status Reports
• Results
Table 2.2: The basic components of a GAMS model
5. As you can see from the list of input components above, the creation of GAMS entities involves two
steps: a declaration and an assignment or definition. Declaration means declaring the existence of
something and giving it a name. Assignment or definition means giving something a specific value or
form. In the case of equations, you must make the declaration and definition in separate GAMS
statements. For all other GAMS entities, however, you have the option of making declarations and
assignments in the same statement or separately.
6. The names given to the entities of the model must start with a letter and can be followed by up to
thirty more letters or digits.
2.3 Sets
Sets are the basic building blocks of a GAMS model, corresponding exactly to the indices in the algebraic
representations of models. The Transportation example above contains just one Set statement:
Sets
i canning plants / seattle, san-diego /
j markets / new-york, chicago, topeka / ;
The effect of this statement is probably self-evident. We declared two sets and gave them the names i and j. We
also assigned members to the sets as follows:
i = {Seattle, San Diego}
j = {New York, Chicago, Topeka}.
You should note the typographical differences between the GAMS format and the usual mathematical format
for listing the elements of a set. GAMS uses slashes ’/’ rather than curly braces ’{}’ to delineate the set simply