Algebraic nature of variable and equation specifications

When one moves to algebraic modeling the variable and equation declarations can have an added element of set dependency as illustrated in our examples and reproduced below

 constraint(i) ;

 Qd(commodities)

 Qs(commodities) ;

 PSupply(commodities)

 Equilibrium(commodities)  ;

Such definitions indicate that these variables and equations are potentially defined for every element of the defining set (also called the domain) thus x could exist for each and every element in j.  However the actual definition of variables does not occur until the .. equation specifications are evaluated as discussed next.  More on set dependent variable and equation definitions appears in the Variables, Equations, Models and Solves chapter.