General expression : min_ or max_
AnsweredHi,
I wanted to use min_ expression in the rhs of constraint (please see the below expression, schedule[i] is decision variable).
model.addConstr(quicksum(100*schedule[i] for i in index) <= 100  min_(100, quicksum(100 for i in index if i.id==0)))
However I had TypeError which is unsupported operand type for : 'int and 'GenExpr'.
Thus, I changed the above expression as below.
model.addConstr(quicksum(100  100*schedule[i] for i in index) >= min_(100, quicksum(100 for i in index if i.id==0)))
Now I have GurobiError that General expressions can only be used for equality constraint.
Would you please help me how I can solve this issue?
Thanks,

The min_() helper function can only be used to set one variable equal to a group of variables and/or constants. This would be used if, e.g., you want to add a constraint like \( x = \min\{y, z, 2\} \), where \(x\), \(y\), and \(z\) are variables.
In your case, the elements of \( \texttt{index} \) are not variables. Thus, the minimum of \( \texttt{100} \) and \( \texttt{sum(100 for i in index if i.id == 0)} \) is a constant value that doesn't depend on any variables. This means you can use Python's builtin \( \texttt{min()} \) function:
model.addConstr(quicksum(100*schedule[i] for i in index) <= 100  min(100, sum(100 for i in index if i.id == 0)))
Note that I used Python's builtin \( \texttt{sum()} \) function instead of Gurobi's quicksum() function. The latter returns a LinExpr object, which won't work well with \( \texttt{min()} \).
0 
Thank you Eli for your help!
0
Please sign in to leave a comment.
Comments
2 comments