Aid with initial formulation and subsequent changes

GAMS aids both in initially formulating and subsequently revising formulations.  GAMS facilitates specification and debugging of an initial formulation by allowing the modeler to begin with a small data set, then after verifying correctness expand to a much broader context.  For example, one could initially specify a small transportation model with a few suppliers and demanders. Then after that model is debugged one could expand the problem to encompass fifty shipping origins and two hundred destinations without needing to change the algebraic model as discussed in the Small to Large: Aide in Development and Debugging chapter and the expandability section above.

GAMS also makes it easy to alter the model.  Large models in programs like spreadsheets can be difficult to modify.  In a spreadsheet, I find it hard to add in a set of new constraints and variables properly interjecting all the linkages and cannot figure out how to easily get a model right with a few commodities then automatically expand the model scope to many commodities and locations as illustrated in the expandability section above.  On the other hand, GAMS allows one to add model features much more simply.  Generally, modelers do not try to make a complete formulation the first time around.  Rather one starts with a small formulation and then adds structural features as needed adding features as illustrated in the augmentation section above.  GAMS also enforces consistent modeling, allowing models to be transferred between problem contexts as shown above.