Quick start - Gams

Notes
The general form of these statements are
Equations comma or line feed specified list of equations ;
where equation or equations is required
a list of equations follows
a ; ends the statement
In optimization models the objective function is always defined in one of the named
equations.
This statement may be more complex including set element definitions (as we will
elaborate on below) and descriptive text as illustrated in the file (model.gms)
EQUATIONS
TCOSTEQ TOTAL COST ACCOUNTING EQUATION
SUPPLYEQ(SUPPLYL) LIMIT ON SUPPLY AVAILABLE AT A SUPPLY POINT
DEMANDEQ(MARKET) MINIMUM REQUIREMENT AT A DEMAND MARKET
BALANCE(WAREHOUSE) WAREHOUSE SUPPLY DEMAND BALANCE
CAPACITY(WAREHOUSE) WAREHOUSE CAPACITY
CONFIGURE ONLY ONE WAREHOUSE;
as discussed in the Variables, Equations, Models and Solves chapter.
The equation names can be up to 31 characters long as discussed and illustrated in the
Rules for Item Names, Element names and Explanatory Text chapter.
.. specifications
The GAMS equation specifications actually consist of two parts. The first part naming equations,
was discussed just above. The second part involves specifying the exact algebraic structure of
equations. This is done using the .. notation. In this notation we give the equation name
followed by a .. then the exact equation type as it should appear in the model. The equation
type specification involves use of a special syntax to tell the exact form of the relation involved.
The most common of these are (see the Variables, Equations, Models and Solves chapter for a
complete list):
=E= is used to indicate an equality relation
=L= indicates a less than or equal to relation
=G= indicates a greater than or equal to relation
This is used in each of the example models where a few of the component equations are
reproduced below
OBJ.. Z =E= 109*Xcorn + 90*Xwheat + 115*Xcotton; (optimize.gms)
land.. Xcorn + Xwheat + Xcotton =L= 100;
Courtesy of B.A. McCarl, October 2002 8