how to check if a set is empty

Problems with syntax of GAMS
yanzhiping
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how to check if a set is empty

Postby yanzhiping » 4 months ago

I want to check if a set A is empty or not. If it is empty, then no equation Q(A).
how can I modify the following code?

set A;
equation Q(A);
variable d;
Q(A)$A..
d =E= 0;

cladelpino
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Re: how to check if a set is empty

Postby cladelpino » 4 months ago

Q(A)$A.. is very redundant.

Just with Q(A).. Equation Q will be written one time for each member of A.

If A is empty, it will never be written. Remember that you can only have empty sets if you choose option $Onempty, indicate dimension and have empty bars. Take this example:

$Onempty

set A(*) / /;

variable d;

equation Q,dummy;

Q(A).. d =E= 0;
dummy.. d=l=2;

model p /all/;

solve p using lp maximizing d


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