Originally posted by: BhavnaJha

How do I code an eqn which represents flow balance like     

sum (q in 1..n) x[q][i][j] == sum (p in 1..n) y[i][p][j]  ;  for all i and j

When I code it like this , it executes it as, 

sum (q in 1..n) ( x[q][i][j] == sum (p in 1..n) y[i][p][j] ) //Sums over this whole expression 

What I want it to do is, 

(sum (q in 1..n)  x[q][i][j] ) ==  ( sum (p in 1..n) y[i][p][j] ) 

Will putting parantheses help? 

I did put them but output is still the same, as in I think it is still evaluating it in the previous way. 

Hi,

this looks fine but you may use asser to double check sometimes:

int n=2;

dvar int x[1..n][1..n][1..n] in 0..10;
dvar int y[1..n][1..n][1..n] in 0..10;

subject to

{

forall(i in 1..n,j in 1..n)
  sum (q in 1..n) x[q][i][j] == sum (p in 1..n) y[i][p][j]  ;  
 
 
}

assert forall(i in 1..n,j in 1..n)
  sum (q in 1..n) x[q][i][j] == sum (p in 1..n) y[i][p][j]  ;

regards