Hi,

If you need to use x(i,j) and x(j,i), then you should not declare variable x with domain (i,j). If sets i and j both describe subsets of nodes, you can declare a superset of nodes and make i and j subsets of this superset. Then you can declare x over the superset of all nodes and should be good, e.g.

```
Sets
n superset of nodes /x1,x2,x3,x4,x5, r1,r2,r3,r4,r5/
i(n) subset of nodes /x1,x2,x3,x4,x5/
j(n) subset of nodes /r1,r2,r3,r4,r5/
[...]
Positive Variable
x(n,n) Amount of flow between nodes;
[...]
```

There are many more errors in your model and I guess only you can know how to fix them because only you know what you want to model. E.g. in

```
C2(j).. sum((i),AH(i,j)*x(i,j)) =E= BT(i,j)*sum((i),x(j,i));
```

the i in BT(i,j) is not controlled which is why you get the following error.

```
179 C2(j).. sum((i),AH(i,j)*x(i,j)) =E= BT(i,j)*sum((i),x(j,i));
**** $149
**** 149 Uncontrolled set entered as constant
```

Further errors again about domain violations.

```
181 C4(j).. sum((i),x(i,j)) =L= g(j)*v(j);
**** $171 $171
**** 171 Domain violation for set
```

You declare g over set i but then you use it only with set j as index. The same applies for variable v.

The rest of your model is repeating the same errors in various combinations again and again. Please make sure you understand what those errors mean, e.g. by looking at the tutorial about fixing compilation errors and then try to resolve one error after the other.

Good luck!

Fred