I'm trying to write a Pyomo model where I have a set of variables, indexed by a j in {1,2,...,N} and, for every j, a i in {1,...,N_j}.
My code right now is:
n0=28
n1=8
n2=8
n3=8
n4=10
N=[n0, n1, n2, n3, n4]
rN=range(5)
model = ConcreteModel()
model.J = [RangeSet(1,N[i]) for i in rN]
model.X = [Var(model.J[i], within=NonNegativeReals) for i in rN]
When I try to access a variable, I get the error:
>>>model.X[0][0]
Traceback (most recent call last):
File "<ipython-input-177-297a76d94388>", line 1, in <module>
model.X[0][0]
File "/path/anaconda3/lib/python3.7/site-
packages/pyomo/core/base/indexed_component.py", line 374, in __getitem__
self._not_constructed_error(index)
File "/path/anaconda3/lib/python3.7/site-
packages/pyomo/core/base/indexed_component.py", line 520, in _not_constructed_error
"not been constructed." % (self.name, idx_str,))
ValueError: Error retrieving component IndexedVar[1]: The component has not been constructed.
I think that the error may be that I can't write variables in a list, but I can't think about any other solution.
You have 2 choices.... either construct a set manually with the indices that you want (my example below) and use that throughout the model, or you can can (carefully) only create/call legal indices when you use I and J by looping or making legal indices on the fly.
# ragged set
from pyomo.environ import *
model = ConcreteModel()
# SETS
model.J = Set(initialize=range(3))
model.I = Set(initialize=range(3))
# construct the ragged set
ij = [(i, j) for j in range(3) for i in range(j + 1)]
model.IJ = Set(within=model.I * model.J, initialize=ij)
# VARIABLE
model.x = Var(model.IJ, domain=NonNegativeReals)
model.pprint()
4 Set Declarations
I : Dim=0, Dimen=1, Size=3, Domain=None, Ordered=False, Bounds=(0, 2)
[0, 1, 2]
IJ : Dim=0, Dimen=2, Size=6, Domain=IJ_domain, Ordered=False, Bounds=None
[(0, 0), (0, 1), (0, 2), (1, 1), (1, 2), (2, 2)]
IJ_domain : Dim=0, Dimen=2, Size=9, Domain=None, Ordered=False, Bounds=None
Virtual
J : Dim=0, Dimen=1, Size=3, Domain=None, Ordered=False, Bounds=(0, 2)
[0, 1, 2]
1 Var Declarations
x : Size=6, Index=IJ
Key : Lower : Value : Upper : Fixed : Stale : Domain
(0, 0) : 0 : None : None : False : True : NonNegativeReals
(0, 1) : 0 : None : None : False : True : NonNegativeReals
(0, 2) : 0 : None : None : False : True : NonNegativeReals
(1, 1) : 0 : None : None : False : True : NonNegativeReals
(1, 2) : 0 : None : None : False : True : NonNegativeReals
(2, 2) : 0 : None : None : False : True : NonNegativeReals
5 Declarations: J I IJ_domain IJ x
[Finished in 2.5s]