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Error with lists

Answered
ghada ouerfelli
  • Gurobi-versary
  • Conversationalist
  • First Question 
import numpy as np
import pandas as p
# Parameters and Data
products=["prod1","prod2","prod3","prod4"] # number of products
months=["Jan","Fev","Mar","Apr","May"] #number of periode
Dem_client={
    "Jan":{"prod1":0,"prod2":0,"prod3":0,"prod4":0},
    "Fev":{"prod1":0,"prod2":20,"prod3":0,"prod4":10},
    "Mar":{"prod1":10,"prod2":0,"prod3":0,"prod4":0},
    "Apr":{"prod1":0,"prod2":0,"prod3":0,"prod4":0},
    "May":{"prod1":0,"prod2":0,"prod3":15,"prod4":25}

}
Cout_stockage= {
    "Jan":{"prod1":1,"prod2":6,"prod3":2,"prod4":2},
    "Fev":{"prod1":2,"prod2":9,"prod3":1,"prod4":2},
    "Mar":{"prod1":5,"prod2":5,"prod3":4,"prod4":1},
    "Apr":{"prod1":1,"prod2":1,"prod3":1,"prod4":1},
    "May":{"prod1":2,"prod2":2,"prod3":3,"prod4":4}}
Cout_chan={
    "Jan":{"prod1":2,"prod2":1,"prod3":8,"prod4":1},
    "Fev":{"prod1":5,"prod2":3,"prod3":9,"prod4":2},
    "Mar":{"prod1":8,"prod2":2,"prod3":7,"prod4":1},
    "Apr":{"prod1":3,"prod2":4,"prod3":7,"prod4":1},
    "May":{"prod1":9,"prod2":1,"prod3":4,"prod4":3}}

L=100# capacité limite de production

# importing gurobipy package
from gurobipy import *
# creating an optimization model
mdl=Model('LSP')
# add decision variables
x=mdl.addVars(months,products,name="x")
s=mdl.addVars(months,products,obj=Cout_stockage,name="s")
y=mdl.addVars(months,products,obj=Cout_chan,vtype=GRB.BINARY,name="y")

#define the objective function
mdl.modelSense = GRB.MINIMIZE
#mdl.setObjective(obj, GRB.MINIMIZE)
mdl.setObjective(0, GRB.MINIMIZE)

#factory.setObjective(obj, GRB.MAXIMIZE)
# Add constraints
mdl.addConstrs((x.sum(month,'*') <=L )for month in months)
mdl.addConstrs((x[month,product]<=L*y[month,product]) for month in months for product in products)
mdl.addConstrs((s[month-1,product]+x[month,product])==(Dem_client[month][product]+s[month,product])
for month in range(len(months)) for product in range(len(products)) if month >=1)
mdl.optimize()

the error is:

mdl.addConstrs((s[month-1,product]+x[month,product])==(Dem_client[month][product]+s[month,product])
KeyError: (0, 0)

0

Comments

5 comments

Date Votes
  • Official comment
    Ronald van der Velden
    • Gurobi Staff

    Hi,

    The reason this doesn't work, is because the keys for variable s are not numbers, but codes for the month and product. When you create your constraint, you try and use numbers and this doesn't work.

    The specific error shows that you're trying to access an element of variable s with keys (0, 0) while you should instead access s["Jan", "prod1"]. The best way to achieve this, is by reusing the lists products and months when you create your constraint.

    Best regards,
    Ronald

  • Official comment
    Simranjit Kaur
    • Gurobi Staff
    This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
  • ghada ouerfelli
    • Gurobi-versary
    • Conversationalist
    • First Question

    thanks, Sir but I didn't understand how to reuse the lists of products and months when I create my constraint, can you write the correct constraint, please.

    0
  • ghada ouerfelli
    • Gurobi-versary
    • Conversationalist
    • First Question

    I still have problem :  mdl.addConstrs((s[months[index_month-1],product]+x[month,product])==(Dem_client[month][product]+s[month,product])
    ValueError: too many values to unpack (expected 2)

    import numpy as np
    import pandas as p
    # Parameters and Data
    products=["prod1","prod2","prod3","prod4"] # number of products
    months=["Jan","Fev","Mar","Apr","May"] #number of periode
    Dem_client={
        "Jan":{"prod1":0,"prod2":0,"prod3":0,"prod4":0},
        "Fev":{"prod1":0,"prod2":20,"prod3":0,"prod4":10},
        "Mar":{"prod1":10,"prod2":0,"prod3":0,"prod4":0},
        "Apr":{"prod1":0,"prod2":0,"prod3":0,"prod4":0},
        "May":{"prod1":0,"prod2":0,"prod3":15,"prod4":25}

    }
    Cout_stockage= {
        "Jan":{"prod1":1,"prod2":6,"prod3":2,"prod4":2},
        "Fev":{"prod1":2,"prod2":9,"prod3":1,"prod4":2},
        "Mar":{"prod1":5,"prod2":5,"prod3":4,"prod4":1},
        "Apr":{"prod1":1,"prod2":1,"prod3":1,"prod4":1},
        "May":{"prod1":2,"prod2":2,"prod3":3,"prod4":4}}
    Cout_chan={
        "Jan":{"prod1":2,"prod2":1,"prod3":8,"prod4":1},
        "Fev":{"prod1":5,"prod2":3,"prod3":9,"prod4":2},
        "Mar":{"prod1":8,"prod2":2,"prod3":7,"prod4":1},
        "Apr":{"prod1":3,"prod2":4,"prod3":7,"prod4":1},
        "May":{"prod1":9,"prod2":1,"prod3":4,"prod4":3}}

    L=100# capacité limite de production

    # importing gurobipy package
    from gurobipy import *
    # creating an optimization model
    mdl=Model('LSP')
    # add decision variables
    x=mdl.addVars(months,products,name="x")
    s=mdl.addVars(months,products,obj=Cout_stockage,name="s")
    y=mdl.addVars(months,products,obj=Cout_chan,vtype=GRB.BINARY,name="y")

    #define the objective function
    mdl.modelSense = GRB.MINIMIZE
    #mdl.setObjective(obj, GRB.MINIMIZE)
    mdl.setObjective(0, GRB.MINIMIZE)

    #factory.setObjective(obj, GRB.MAXIMIZE)
    # Add constraints
    mdl.addConstrs((x.sum(month,'*') <=L )for month in months)
    mdl.addConstrs((x[month,product]<=L*y[month,product]) for month in months for product in products)
    mdl.addConstrs((s[months[index_month-1],product]+x[month,product])==(Dem_client[month][product]+s[month,product])
    for month,index_month in months for product in products if month!=months[0])
    mdl.optimize()
    0
  • Jaromił Najman
    • Gurobi Staff

    This has been discussed in Erreur in my code with gurobipy.

    0

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