Divide by variable technique didn't work.

Answered

Thunwa Wanphian

June 17, 2022 09:57

• 
• 
• 

I am trying to divide by decision variable by using the technique from

"How do I divide by a variable in Gurobi?"

Unfortunately it didn't work out well, so I am not sure that where is my mistake.

Noted here: y[j,k] is my decision variable and z[j,k] is an auxiliary variable to define as z[j,k] = 1/y[j,k].

Auxiliary_noise = m.addConstrs((z[j,k]*y[j,k] == 1 for j in Machines for k in Times), name = "Aux_Noise")

#Expo_noise_matrix having only 1 - Times = 1-16
Expo_noise_matrix = {}
Aux_Expo_noise1 = {}
Aux_Expo_noise2 = {}
for k in Times:
    Aux_Expo_noise1[k] = (70*y[1,k]+60*y[2,k]+80*y[3,k])*(z[1,k]+z[2,k]+z[3,k])
    Aux_Expo_noise2[k] = 0.8+0.2*y[1,k]+0.2*y[2,k]+0.2*y[3,k]
    Expo_noise_matrix[k] = (Aux_Expo_noise[k]*Aux_Expo_noise2[k])

Here is the results.

<ipython-input-59-b16dfe9cfed7> in <module>
     27     Aux_Expo_noise1[k] = (70*y[1,k]+60*y[2,k]+80*y[3,k])*(0.01+z[1,k]+z[2,k]+z[3,k])
     28     Aux_Expo_noise2[k] = 0.8+0.2*y[1,k]+0.2*y[2,k]+0.2*y[3,k]
---> 29     Expo_noise_matrix[k] = (Aux_Expo_noise[k]*Aux_Expo_noise2[k])

src\gurobipy\quadexpr.pxi in gurobipy.QuadExpr.__mul__()

src\gurobipy\quadexpr.pxi in gurobipy.QuadExpr._mul()

GurobiError: Invalid argument to QuadExpr multiplication

I am not sure what i did wrong and if you have any recommendations, please let me know,

 

Best regards,

Thunwa 

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 16, 2025 23:34

  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.
• 

  Marika Karbstein

  • Gurobi Staff

  June 17, 2022 12:43

  Hi Thunwa,

  I am not quite sure about your model.
  But you need to use the m.addVars() method to create variables for Aux_Expo_noise1[k] and Aux_Expo_noise2[k] and also for Expo_noise_matrix[k] (if this should not be just 1).

  Then you need to add a constraint for each line in your for-loop, for example (here I assume matrix[k] needs to be 1):

  aux1 = m.addVars(Times, vtype=gp.GRB.CONTINUOUS, name = "aux1")
  aux2 = m.addVars(Times, vtype=gp.GRB.CONTINUOUS, name = "aux2")
  for k in Times:
      m.addConstr(aux1[k] == (70*y[1,k]+60*y[2,k]+80*y[3,k])*(z[1,k]+z[2,k]+z[3,k]))
      m.addConstr(aux2[k] == 0.8+0.2*y[1,k]+0.2*y[2,k]+0.2*y[3,k])
      m.addConstr(aux1[k] * aux2[k] == 1)

  I hope this information helps.

  Best regards,
  Marika

  0
• 

  Thunwa Wanphian

  June 20, 2022 02:42

  • 
  • 
  • 

  Hi, Marika

   

  This is really informative to my model.

  Thank you a lot

   

  Best regards,

  Thunwa

  0

Post is closed for comments.