The WHILE statement is used in order to loop over a block of statements.

Syntax

The syntax is:

   WHILE (condition,
          statements;
         );

Warning: One cannot make declarations or define equations

       inside a WHILE statement. 

Example 1

One can use WHILE statements to control the SOLVE statement. For instance, consider the following bit of GAMS code that randomly searches for a global optimum of a nonconvex model:

   scalar count ;
   count = 0 ;
   while((count le 1000),
           x.l(j) = uniform(0,1) ;
           option bratio = 1 ;
           solve ml using lp minimizing obj ;
           if (obj.l le globmin,
               globmin = obj.l ;
               globinit(j) = x.l(j) ;
              ) ;
           count = count + 1 ;
         ) ;

In this example, a non-convex model is solved from 1000 random starting points, and the global solution is tracked.

Example 2

The model PRIME in the model library illustrates the use of the WHILE statement through an example where the set of prime numbers less than 200 are generated

Example 3

The following GAMS code is illegal since one cannot define equations inside a WHILE statement.

   While (s GT 0,
            eq.. sum(i,x(i)) =g= 2 ;
         );

Example 4

The following GAMS code is illegal since one cannot make declarations inside a WHILE statement.

   WHILE (s gt 0,
            scalar y ; y = 5 ;
          );