I just started working with pyomo framework and python. I am trying to solve simple models. And when I formulate the objective function, I receive the following error before when run the code
KeyError: (0, 0)
Here is the formulation of the problem: Formulation
And the code:
from pyomo.environ import *
N = 3
M = 4
P = 3
d = {(1, 1): 1.7, (1, 2): 7.2, (1, 3): 9.0, (1, 4): 8.3,
(2, 1): 2.9, (2, 2): 6.3, (2, 3): 9.8, (2, 4): 0.7,
(3, 1): 4.5, (3, 2): 4.8, (3, 3): 4.2, (3, 4): 9.3}
seq = ConcreteModel()
seq.Locations = range(N) #Set N
seq.Customers = range(M) #Set M
seq.x = Var(seq.Locations, seq.Customers, bounds=(0.0, 1.0)) #x[n,m]
seq.y = Var(seq.Locations, within=Binary)
seq.obj=Objective(expr = sum( d[n,m]*seq.x[n,m] for n in seq.Locations for m in seq.Customers))
seq.single_x = ConstraintList()
for m in seq.Customers:
seq.single_x.add(
sum(seq.x[n,m] for n in model.Locations ) == 1.0)
seq.bound_y = ConstraintList()
for n in seq.Locations:
for m in seq.Customers:
seq.bound_y.add( seq.x[n,m] <= seq.y[n] )
seq.num_facilities = Constraint(
expr=sum( seq.y[n] for n in seq.Locations) == P)
What could be an issue? Thank you!
The key error you are getting is due to the fact that your dictionary d doesn't have an entry for [0, 0].
My recommendation is that you bring everything into the model (see my edits below). That way you can "pretty print" the model, which makes it super easy to troubleshoot while building.
Good luck!
from pyomo.environ import *
N = 3
M = 4
P = 3
d = {(1, 1): 1.7, (1, 2): 7.2, (1, 3): 9.0, (1, 4): 8.3,
(2, 1): 2.9, (2, 2): 6.3, (2, 3): 9.8, (2, 4): 0.7,
(3, 1): 4.5, (3, 2): 4.8, (3, 3): 4.2, (3, 4): 9.3}
seq = ConcreteModel()
### SETS
seq.Locations = Set(initialize = list(range(1, N+1))) #Set N # note the capitalization Set, the pyomo type
seq.Customers = Set(initialize = list(range(1, M+1))) #Set M
### PARAMS
seq.d = Param(seq.Locations, seq.Customers, initialize=d)
### VARS
seq.x = Var(seq.Locations, seq.Customers, bounds=(0.0, 1.0)) #x[n,m]
seq.y = Var(seq.Locations, within=Binary)
seq.obj=Objective(expr = sum( seq.d[n,m]*seq.x[n,m] for n in seq.Locations for m in seq.Customers))
seq.single_x = ConstraintList()
for m in seq.Customers:
seq.single_x.add(
sum(seq.x[n,m] for n in seq.Locations ) == 1.0)
seq.bound_y = ConstraintList()
for n in seq.Locations:
for m in seq.Customers:
seq.bound_y.add( seq.x[n,m] <= seq.y[n] )
seq.num_facilities = Constraint(
expr=sum( seq.y[n] for n in seq.Locations) == P)
seq.pprint()