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python-3.xpyomo

'SumExpression' object is not iterable

i am trying an opimization problem in pyomo...i get 'SumExpression' object is not iterable error at line(model.nt[j] = model.ntm1[j] + ....)... as shown in below code R_2_j(), R_1_j() function outputs depend on decision variables...if i make model.nt a parameter it shows because of decision variable involved t is not i real domain so i made model.nt a set now and also can i not do this ""model.ntm1[j] + model.q[j]*R_2_j(model, j, -1)"" like to multiply and add function and model...if so what should i do about it ...and also since model.nt involves decision variables should i keep model.nt a set or a param or a var

model.q = Param(model.l,
                 initialize={2: 0.235,
                             4: 0.235,
                             6: 0.235,
                             8: 0.235},
                 doc='q')
model.nt = Set(model.l)
model.ntm1 = Param(model.l,
                 initialize={2: 0,
                             4: 0,
                             6: 0,
                             8: 0},
                 doc='queuesmm1')
for j in model.l:
  model.nt[j] =  model.ntm1[j] + model.q[j]*R_2_j(model, j, -1) + model.q[j]*(R_1_j(model,j, 0) + G_e_j(model,j, 0)) - model.s[j]*G_e_j(model,j, 0)
Solution

    1. If I understand what you are trying to do, you are trying to make a set (nt) depend on the value of some variables through R_2_j. This is not a valid formulation, all sets and parameters values must be independent of variables (but can depend on other parameters!).

    2. I think in a couple of instances you are trying to use an implicit product, e.g. model.q[j]R_2_j(model, j, -1). If what you are trying to obtain is a product, you need to write it explicitly:

      model.q[j] * R_2_j(model, j, -1)

      (notice the *)

      There's at least another case in the same row.