data_import / syntax error
AnsweredHello,
I have a very simple, quick question! I want to use a not complete graph in my MIP model, how can I model the edges?
for example: I can't use E = [(i,j) for i in S for j in T]
and I have a list of edges that I need to use like: E=[(1,16),
(1,23),
(1,25),
(1,26),
(2,17),
...]
Here is the error:
File "model.pxi", line 3332, in gurobipy.Model.addConstrs
File "MIP.py", line 283, in <genexpr> m.addConstrs(x[i,p]+y[j,p] <= 1 + z[i,j,p] for i,j in E for p in K )
KeyError: (17, 1)
The error must come from this part:for i,j in E, how do I define that i , j are the first and second element in E according to the imported data?
Here is the semi_complete code :
S_size =15
T_size =15
k_numb =3
S=[s_i for s_i in range(1,S_size+1) ]
T=[t_j for t_j in range(1,T_size+1) ]
K=[k_nb for k_nb in range(1,k_numb+1) ]
#E = [(i,j) for i in S for j in T]
E=[(1,16),
(1,23),
(1,25),
...]
E_complete = [(1,17),
(1,18),
(1,19),
..]
B = [(i,p) for i in S for p in K]
C = [(j,p) for j in T for p in K]
D = [(i,j,p) for i,j in E_complete for p in K]
m = gp.Model("ILPM")
x = m.addVars(B , name="x")
y = m.addVars(C , name="y")
z = m.addVars(D , name="z")
x.vType = GRB.BINARY
y.vType = GRB.BINARY
z.vType = GRB.BINARY
m.modelSense = GRB.MINIMIZE
m.setObjective(gp.quicksum(z[i,j,p] for i,j in E_complete for p in K))
m.addConstrs(x[i,p]+y[j,p] <= 1 + z[i,j,p] for i,j in E_complete for p in K )
m.addConstrs(gp.quicksum(x[i,p] for p in K)==1 for i in S)
m.addConstrs(x[i,p] <= y[j,p] for i,j in E for p in K )
m.optimize()
m.printAttr('x')
Thank you
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Gurobi Staff
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Hi,
You see this error because you are trying to add the variable y[17,1] to a constraint, but this variable does not exist. A y variable is defined for every tuple in the list C:
[(1, 1), (1, 2), (1, 3), (2, 1), (2, 2), (2, 3), (3, 1), (3, 2), (3, 3),
(4, 1), (4, 2), (4, 3), (5, 1), (5, 2), (5, 3), (6, 1), (6, 2), (6, 3),
(7, 1), (7, 2), (7, 3), (8, 1), (8, 2), (8, 3), (9, 1), (9, 2), (9, 3),
(10, 1), (10, 2), (10, 3), (11, 1), (11, 2), (11, 3), (12, 1), (12, 2),
(12, 3), (13, 1), (13, 2), (13, 3), (14, 1), (14, 2), (14, 3), (15, 1),
(15, 2), (15, 3)]Note that (17,1) is not in this list. Consider the following constraint set:
m.addConstrs(x[i,p]+y[j,p] <= 1 + z[i,j,p] for i,j in E_complete for p in K)We encounter the error for the first of these constraints, defined by (i,j) = (1,17) in E_complete and p = 1 in K, because y[j,p] is never defined.
Could you elaborate on what these variables represent and the sets you want to use to define them? Thanks!
Eli
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Hi Eli,
Yes, you are right! I didn't define the sets correctly! that works now!
Thank you so much
Shiva
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