问题
I am trying to solve FLP using PuLP. I want to add logical constraint for variable value.
I have LpVariable f and C is list of LpVariables . I want to add f to the constraint of problem and which depends on values of c[i].
Below is code snippet >
prob = LpProblem("The MILP problem", LpMinimize)
Added 1st constraint :
prob += lpSum(c[i] for i in range (len(c))) == 2
Now I want to add following constraint:
if`lpSum(c[i] for i in range (len(c))) > 1:
` prob += f == 1
else:
prob += f == 0
prob += lpSum(c[i] for i in range (len(c)) + f )
Now problem is LpVariables c[i] are initialized with None
and hence it throws error while calculating lpSum()
.
I hope I am clear. Let me know if need any help in understanding this query but I think given code snippet is sufficient enough.
回答1:
Three points:
(1) Your first constraint forces the lpsum to be equal to 2, so f will always be 1 in your example - are you sure your formulation is correct?
(2) If statements can't be used in combination with the lpSum - you should formulate it as an actual constraint.
For example, you could define f as a binary variable and add this constraint:
prob += lpSum(c[i] for i in range (len(c))) - 1 <= M*f
where M is a sufficiently large number. Then, if f==0 we have that "lpsum() <= 1" and if f==1 we have that lpsum can be anything. Play around with that type of constraints to get f to behave the way you want.
(3) The constraint "prob += lpSum(c[i] for i in range (len(c)) + f )" does nothing unless it's supposed to be the objective of your MILP? If so, you should add it immediately after prob = LpProblem("The MILP problem", LpMinimize)
Good luck
来源:https://stackoverflow.com/questions/33360898/how-to-add-logical-constraints-in-pulp