[Help-glpk] constraint variable only 0.

[Joko Bintarto]

the constraint in my code like this

 ...

var u {i in 1..CM, j in 1..TM} binary;
var x {i in 1..CM} integer; #1 if x[i] = j and 0 otherwise
...
minimize cost: sum{i in 1..CM, j in TM} u[i,j];
...
s.t. pret1 {i in 1..CM, j in 1..TM} : (x[i]-j) + TM*u[i,j] <= TM;
...

data;
param CM := 20;
param TM := 30;
...

help me, why u consists only 0. there are 1 in matrix x.