Say a vector *x* has ten values (decision variables). Objective: Maximize the sum of *x*. How do I model this constraint: The sum of consecutive four elements in the vector should be less than 10.

You can use the lag and lead operator as in the following example:

```
Set i /1*10/; Alias (i,j);
Set iconseq(i,j);
Scalar cnt;
loop(i, for(cnt=0 to 3, iconseq(i,i+cnt) = yes));
display iconseq;
Variable x(i);
Equation e(i);
e(i).. sum(iconseq(i,j), x(i)) =l= 10;
```

If you want your constraint to interpret “consecutive” in a circular manner, you will have to replace + in the loop-statement by ++ like this:

```
loop(i, for(cnt=0 to 3, iconseq(i,i++cnt) = yes));
```