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I have an optimization problem that consists of reducing the price/weight of the shipping of the products as much as possible. I modeled as below: MATHEMATICAL MODEL

Basically, I have a vector called order, which represents the weight of each order to be delivered. There is a vector w, which represents the weight of each truck, a vector p which represents the price that transport costs using each one of them. And a variable n, which represents a maximum number of customers on a delivery route.

I'm trying to use Gurobi as a solver but I'm getting the following error:

TypeError                                 Traceback (most recent call last)
src/gurobipy/var.pxi in gurobipy.Var.__truediv__()

TypeError: float() argument must be a string or a number, not 'generator'

During handling of the above exception, another exception occurred:

GurobiError                               Traceback (most recent call last)
<ipython-input-5-18654dbac5a8> in <module>

---> 30 m.setObjective( gp.quicksum((z_n[i]/(gp.quicksum(x[i][j] *order[j]) for j in range(numItems))) for i in range(numTrucks)) , GRB.MINIMIZE)

src/gurobipy/gurobi.pxi in gurobipy.quicksum()

<ipython-input-5-18654dbac5a8> in <genexpr>(.0)
---> 30 m.setObjective( gp.quicksum((z_n[i]/(gp.quicksum(x[i][j] *order[j]) for j in range(numItems))) for i in range(numTrucks)) , GRB.MINIMIZE)

src/gurobipy/var.pxi in gurobipy.Var.__truediv__()

GurobiError: Divisor must be a constant

Follow the implemented code:

w = [650,1200,1200,1200,1200,1800,1800,1800,1800]
p = [250,330, 330, 330, 330, 400, 400, 400,400  ]
n = 7
order = [288,61,91,65,103,114,71,392,80,306,749,159,149,204,64,45,156,110,562,96,295,75,465,51,54,414,52,571,73,286,96,325,81,111,138,13,105,112,60,52,70,238,519,305,117,222,112,26,54,26,131,73,63,249,144,44,15,275,302]
numTrucks = len(w)
numItems = len(order)



import gurobipy as gp
from gurobipy import GRB
import itertools

m = gp.Model('trucks optimization')

x = m.addVars(numTrucks, numItems, vtype=gp.GRB.BINARY, name="x")
z_n = m.addVars(numTrucks, name="z_n")
  
m.addConstrs(gp.quicksum(x[i,j] for j in  range(numItems)) <= n for i in range(numTrucks))
m.addConstrs(gp.quicksum(x[i,j] for i in range(numTrucks)) == 1 for j in range(numItems))
m.addConstrs(gp.quicksum(x[i,j] * order[j] for j in range(numItems)) <= w[i] for i in range(numTrucks))
m.addConstrs(z_n[i] == p[i] for i in range(numTrucks))

m.setObjective( gp.quicksum((z_n[i]/(gp.quicksum(x[i][j] *order[j]) for j in range(numItems))) for i in range(numTrucks)) , GRB.MINIMIZE)

m.optimize()
Fernanda Almeida
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    Welcome to SO! Please [Take the Tour](https://stackoverflow.com/tour), read: [What types of questions should I avoid asking?](https://stackoverflow.com/help/dont-ask), [What topics can I ask about here?](https://stackoverflow.com/help/on-topic) and [How to create a Minimal, Reproducible Example](https://stackoverflow.com/help/minimal-reproducible-example). Please post the entire stacktrace in the question. – Michael Ruth Sep 01 '22 at 23:45
  • Cross-posted: https://stackoverflow.com/q/73576266/781723, https://cs.stackexchange.com/q/153947/755. Please [do not post the same question on multiple sites](https://meta.stackexchange.com/q/64068). – D.W. Sep 02 '22 at 03:43
  • Please work on reducing your code to a minimal, reproducible example. I suspect this can be reduced further. – D.W. Sep 02 '22 at 03:44

0 Answers0