gurobipy.GurobiError: Invalid argument to QuadExpr multiplication

Answered

Aria

• September 11, 2023 08:24
• Edited

Hello,

I've been trying to formulate a basic optimization problem in python,

the warning code are as follows:

la = m.addVars(fullhour, vtype=GRB.CONTINUOUS, name="la", ub=1, lb=0)
ll = m.addVars(fullhour, vtype=GRB.CONTINUOUS, name="ll", ub=1, lb=0)
P = m.addVars(fullhour, vtype=GRB.CONTINUOUS, name="P")
L = m.addVars(fullhour, vtype=GRB.CONTINUOUS, name="L")
for t in range(14):
    m.addConstr(ll[t] == la[t] * la[t])
    expr == -1* ll[t] + 7 * la[t] + 0.6
m.addConstr(L[t] == P[t] * expr)

gurobi error:    m.addConstr(L[t] == P1[t] * expr1)
  File "src\gurobipy\quadexpr.pxi", line 555, in gurobipy.QuadExpr.__mul__
  File "src\gurobipy\quadexpr.pxi", line 292, in gurobipy.QuadExpr._mul
gurobipy.GurobiError: Invalid argument to QuadExpr multiplication

How can I solve it? I don't understand if there are any prohibited multilinear terms in the code. Any suggestions will be much appreciated.

Related to

• Bilinear

0

• 

  Jaromił Najman

  Gurobi Staff

  • September 11, 2023 08:52

  Hi Aria,

  I would guess that the issue is about the \(\texttt{expr}\) object.

  You don't assign a value to it but you check for equality, you use \(\texttt{==}\) instead of \(\texttt{=}\).

  Then, the

  m.addConstr(L[t] == P[t] * expr)

  is outside of the \(\texttt{for}\)-loop.

  Instead of using an intermediate \(\texttt{expr}\) object, you could directly model

  m.addConstr(L[t] == P[t] * -1 * ll[t] + 7 * P[t] * la[t] + 0.6 * P[t])

  On a side note: The error seems to not match the snippet, because there is a \(\texttt{expr1}\) in the error which is not present in your snippet.

  Best regards, 
  Jaromił

  1
• 

  Aria

  • September 11, 2023 09:50

  

  

  Hi Jaromił,

  The error messages I was encountering with previous code have been resolved.

  Thank you.

  0

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