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My model is infeasible. Can someone please help me?

Answered

Comments

3 comments

  • Gwyneth Butera
    Gurobi Staff Gurobi Staff

    Hi Jordi - Did you try to compute an IIS as discussed in the Knowledge Base article How do I determine why my model is infeasible?

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  • Jordi Kortekaas
    Curious
    First Comment

    yes, but still it is not very clear to me what is wrong the ISS: 

    \ Model CVRP_copy
    \ LP format - for model browsing. Use MPS format to capture full model detail.
    Minimize
     
    Subject To
     R7: C12 + C13 + C24 + C25 + C36 + C37 + C48 + C49 + C60 + C61 + C72 + C73
       = 1
     R42: C12 + C24 + C36 + C48 + C60 + C72 = 1
     R43: C13 + C25 + C37 + C49 + C61 + C73 = 1
    Bounds
    Binaries
     C12 C13 C24 C25 C36 C37 C48 C49 C60 C61 C72 C73
    End
    AC

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  • Marika Karbstein
    Gurobi Staff Gurobi Staff

    You probably need to define N and V as

        N = [i for i in range(1,n)] # set of clients
        V = [i for i in range(n)] # set of clients plus the depot (depot is 0)
    This would lead to a feasible model. But I think a constraint is missing that the same vehicle is used when arriving at client i and when leaving client i.
    And finally, I think
    # Each vehicle must leave the depot
      mdl.addConstrs(quicksum(x[i, 0, k] for i in V if i != 0) == 1 for k in range(num_vehicles))

    needs to be 

    # Each vehicle must leave the depot
    mdl.addConstrs(quicksum(x[0, i, k] for i in V if i != 0) == 1 for k in range(num_vehicles))
    Then it also fits your evaluation of the solution.
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