Variable specification - suppression

(transbad.gms vs transfix.gms)

Cases can exist where unneeded variables are being defined.  Creation of an unnecessary variable requires excess memory.  For example, in a transport model I may only want variables that are defined over routes with nonzero transportation cost so I enter a conditional on cost.

TCOST =E= SUM((PLANT,MARKET)$cost(plant,market)

          , SHIPMENTS(PLANT,MARKET)*COST(PLANT,MARKET));

fsSUPPLYEQ(PLANT)$supply(plant)..

  SUM(MARKET $cost(plant,market), SHIPMENTS(PLANT, MARKET))=L=SUPPLY(PLANT);

fsDEMANDEQ(MARKET)$demand(market)..

  SUM(PLANT$cost(plant,market),  SHIPMENTS(PLANT, MARKET))=G=DEMAND(MARKET);