Problem with Updating Values in GAMS Equations

Hello,
I have the following code in GAMS, where I want to subtract X from Y and reassign the result back to X. However, I’m not sure what the issue is!

Equation es1(t), es2(t), es3(t), es4(t), es5(t);
Parameters X(*, b);
Variable Y(t, z);
es1(t)..  X(t, '6') =e= Y(t, 'z1') - X(t, '6');
es2(t)..  X(t, '18') =e= Y(t, 'z2') - X(t, '18');
es3(t)..  X(t, '21') =e= Y(t, 'z3') - X(t, '21');
es4(t)..  X(t, '24') =e= Y(t, 'z4') - X(t, '24');
es5(t)..  X(t, '30') =e= Y(t, 'z5') - X(t, '30');

Here:

  • X is a parameter.
  • Y is a variable.
  • Both have numeric values.

When I use the command display Y.l;, I encounter the following error:

Error 141: Symbol declared but no values have been assigned. Check for missing data definition, assignment, data loading or implicit assignment via a solve statement. A wild shot: You may have spurious commas in the explanatory text of a declaration. Check symbol reference list.

However, if I run the display Y.l; command before these equations, it works fine and displays the values without any problem.

I would greatly appreciate it if you could guide me on how to fix this issue.

Thank you!

X is defined in the code as follows, but I forgot to include this part when posting the code here:

Parameters K(b) /1 0, 2 10, 3 20, 4 30, ..., 32 40, 33 50/;
X(t, b) = K(b);