Quick start - Gams

Thisreport(resources,"Marginal","Value")=
available.m(resources);
option thisreport:2:1:2;
display thisreport;
where both equation marginals (shadow prices) and variable levels are included in the report
writing calculations. This yields the report
Total Use by Use by Marginal
Available Corn Wheat Value
Land 100.00 50.00 50.00 52.00
Labor 500.00 300.00 200.00 9.50
where I have color coded the originating statements and resultant output.
The report wring topic is extensively discussed in the Report Writing chapter with a more
advanced discussion also appearing in the Output via Put Commands chapter.
Why use GAMS and algebraic modeling
Finally I feel it is beneficial to examine the attributes and difficulties with GAMS based
algebraic modeling. This is done under the following topics
Use of algebraic modeling
Context changes,
Expandability
Augmenting models
Aid with initial formulation and subsequent changes
Adding report writing
Self-Documenting Nature
Large Model Facilities
Automated Problem Handling
Model Library and widespread professional use
Use by Others
Ease of use with nonlinear, mixed integer, CGE and other problem forms
Interface with other packages
Use of algebraic modeling
GAMS permits one to express a formulation in general algebraic terms using symbolic
summation notation. This allows modelers to concisely state problems, largely independent of
the data and exact application context. Such formulations are inherently expandable, easily
subjected to context changes, and easily augmented as will be discussed just below.
However use of algebraic modeling can be a two edged sword GAMS algebraic requirements
and summation notation are difficult for some users. Some people will always desire to deal
with the exact problem context, not an abstract general formulation. This does lead to a strategy
Courtesy of B.A. McCarl, October 2002 41