Smin , Smax

Expressions can contain a function that calculates the minimum or maximum of set indexed expressions or terms (function.gms)

X=smin(I, a(i)*0.2-0.5);

Eq8..   z=e= smin(I, va(i)*0.2-0.5);

X=smax(I, a(i)*0.2-0.5);

Eq9..   z=e= smax(I, va(i)*0.2-0.5);

This function is not continuous and not smooth.  It can be used on data during GAMS calculation or in models on variables or parameters.  It's use in .. equations in terms that involve variables requires the model type be DNLP or one of the other types that handles nonsmooth functions.  More on Smin and Smax can be found here.