Quick start - Gams

Model statistics ............................................................................................................... 20
Solver report ........................................................................................................................ 20
Solution summary ........................................................................................................... 20
Equation solution report.................................................................................................. 21
Variable solution report .................................................................................................. 22
Exploiting algebra .................................................................................................................... 23
Equation writing – sums...................................................................................................... 23
Revised algebra exploiting optimization example............................................................... 24
Revised equilibrium example .............................................................................................. 25
Dissecting the algebraic model ................................................................................................ 27
Sets....................................................................................................................................... 27
Alias ................................................................................................................................ 28
Data entry ............................................................................................................................ 28
Scalars............................................................................................................................. 28
Parameters....................................................................................................................... 28
Tables.............................................................................................................................. 29
Direct assignment............................................................................................................ 30
Algebraic nature of variable and equation specifications .......................................... 31
Algebra and model .. specifications ........................................................................... 31
Output differences ............................................................................................................... 32
Equation listing ............................................................................................................... 32
Variable list..................................................................................................................... 33
Equation solution report.................................................................................................. 34
Variable solution report .................................................................................................. 34
Good modeling practices.......................................................................................................... 34
Structure of GAMS statements, programs and the ;................................................................. 36
Adding complexity................................................................................................................... 37
Conditionals......................................................................................................................... 37
Conditionally execute an assignment.............................................................................. 37
Conditionally add a term in sum or other set operation.................................................. 37
Conditionally define an equation.................................................................................... 38
Conditionally include a term in an equation................................................................... 38
Displaying data.................................................................................................................... 38
Report writing...................................................................................................................... 40
Why use GAMS and algebraic modeling................................................................................. 41
Use of algebraic modeling................................................................................................... 41
Context changes.............................................................................................................. 42
Expandability .................................................................................................................. 42
Augmentation.................................................................................................................. 43
Aid with initial formulation and subsequent changes ......................................................... 44
Adding report writing .......................................................................................................... 44
Self-documenting nature...................................................................................................... 44
Large model facilities ..........................................................................................................45
Automated problem handling and portability...................................................................... 46
Model library and widespread professional use .................................................................. 46
Use by Others ...................................................................................................................... 46
Courtesy of B.A. McCarl, October 2002 2