Quick start - Gams

POSITIVE VARIABLES P(commodities)
Qd(commodities)
Qs(commodities) ;
EQUATIONS PDemand(commodities)
PSupply(commodities)
Equilibrium(commodities) ;
alias (cc,commodities);
Pdemand(commodities)..
P(commodities)=g=
intercepts("demand",commodities)
+sum(cc,slopes("demand",commodities,cc)*Qd(cc));
Psupply(commodities)..
intercepts("supply",commodities)
+sum(cc,slopes("supply",commodities,cc)* Qs(cc))
=g= P(commodities);
Equilibrium(commodities)..
Qs(commodities)=g= Qd(commodities);
MODEL PROBLEM /Pdemand.Qd, Psupply.Qs,Equilibrium.P/;
SOLVE PROBLEM USING MCP;
Dissecting the algebraic model
Sets
Above we used the subscripts i , j, commodities and cc for addressing the variable, equation and
data items. In GAMS subscripts are SETs. In order to use any subscript one must declare an
equivalent set.
The set declaration contains
the set name
a list of elements in the set (up to 31 characters long spaces etc allowed in quotes)
optional labels describing the whole set
optional labels defining individual set elements
The general format for a set statement is:
SET setname optional defining text
/ firstsetelementname optional defining text
secondsetelementname optional defining text
... /;
Examples
(sets.gms)
SETs j /x1,x2,x3/
i /r1 ,r2/;
SET PROCESS PRODUCTION PROCESSES /X1,X2,X3/;
SET Commodities Crop commodities /
corn in bushels,
wheat in metric tons,
milk in hundred pounds/ ;
More on sets appears in the Sets chapter.
Courtesy of B.A. McCarl, October 2002 27