I am new to gams (so probably a stupid question) and trying to set up a model with the main error being “set is already under control”. I can easily create the model in excel, but can’t here. Here is the following code that I am trying to use to solve whether or not to keep or cull a cow to reach a specific threshold. All the values need to be summed over all cows i. Thanks for all your help!
Set
i cows / cowone, cowtwo, cowthree / ;
Parameters
a(i) net present value of cow i in cases
/ cowone 500
cowtwo 400
cowthree 450 /
b(i) yield of cow i in cases
/ cowone 10000
cowtwo 8000
cowthree 9000 /
c(i) SCC of cow i in cases
/ cowone 5900000
cowtwo 3500000
cowthree 2500000 /
d(i) Cull vlaue of cow i in cases
/ cowone 100
cowtwo 90
cowthree 80 /;
Variables
vc(i) Value of cow i if culled in all cases
vr(i) Value of cow i if retained in all cases
*this is an attempt at a binary constraint
z total net present value ;
Equations
NPV define objective function
SCC(i) SCC for all cows i
Yield(i) milk for all cows i
Mix(i) mix in bulk tank;
NPV … z =e= sum(i, (a(i)*vr(i))+ (d(i)*vc(i)));
SCC(i) … sum(i, vr(i)*c(i)) =E= “SCC”;
Yield(i) … sum(i, vr(i)*b(i)) =E= “Yield”;
Mix(i) … “SCC”/“Yield” =l= 400;
Value … sum(i, vc(i)+vr(i)) =E= 1;
Model dairy /all/ ;
Solve dairy using nlp maximizing z ;
Display y.l, y.m ;
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