Invalid argument to QuadExpr multiplication

Answered

Fatih Dilmit

June 02, 2023 12:41

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I get the error at objective function. The cosole output is:

 File ~\Desktop\Optimization code.py:51 in TSP
    md.setObjective(quicksum(ux[j]*w[0]*z[j]*( tf[0]+tv[0]) for j in range(m)) + quicksum(uy[j]*w[1]*z[j]*(tv[1]+tf[1]) for j in range(m)) +

  File src\gurobipy\gurobi.pxi:3631 in gurobipy.quicksum

  File ~\Desktop\Optimization code.py:51 in <genexpr>
    md.setObjective(quicksum(ux[j]*w[0]*z[j]*( tf[0]+tv[0]) for j in range(m)) + quicksum(uy[j]*w[1]*z[j]*(tv[1]+tf[1]) for j in range(m)) +

  File src\gurobipy\quadexpr.pxi:523 in gurobipy.QuadExpr.__mul__

  File src\gurobipy\quadexpr.pxi:245 in gurobipy.QuadExpr._mul

GurobiError: Invalid argument to QuadExpr multiplication

Can you help me with the problem?

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  Lennart Lahrs

  • Gurobi Staff

  June 02, 2023 13:50 Edited

  Hi Fatih,
  
  Although Gurobi does not directly support constraints containing more general multilinear terms, they can be modeled using a series of bilinear constraints. In your case, you must extend your model by auxiliary variables, to express your objective function using bilinear terms only. Please have a look at this article explaining the concept.

  For further reference, a similar question was asked in these two community posts:
  https://support.gurobi.com/hc/en-us/community/posts/360056771292-Invalid-argument-to-QuadExpr-multiplication-Error-
  https://support.gurobi.com/hc/en-us/community/posts/360076716571-Invalid-argument-to-QuadExpr-multiplication
  
  Best regards,
  Lennart

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