TypeError when using gurobipy.Model.addGenConstrIndicator

Answered

Ludwig Baunach

• May 29, 2024 13:15

Hi, 

I am encountering a problem with a logical constraint. I get the same error when trying ".addGenConstrIndicator". I posted the code below including the error message. I am grateful for any kind of help. Note that this is a test case because I encountered problems in my main model applying a similar logic. The overall goal is to indicate (finish = 1) when beets are finished (beet = 0). 

Thank you!

from gurobipy import Model, GRB, quicksum

# Define the sets I and T
I = [1, 2]
T = [0, 1, 2, 3, 4]

# Create a new Gurobi model
model = Model("test_model")

# Define fixed beet_flow values
beet_flow = {
    (1, 0, 0, 0): 1500.0,
    (1, 0, 0, 1): 5.1,
    (1, 0, 0, 2): 5.0,
    (1, 0, 0, 3): 0.0,
    (1, 0, 0, 4): 0.0,
    (2, 0, 0, 0): 100.5,
    (2, 0, 0, 1): 10.1,
    (2, 0, 0, 2): 10.0,
    (2, 0, 0, 3): 10.0,
    (2, 0, 0, 4): 0.0
}

finish = model.addVars(I, T, vtype=GRB.BINARY, name="finish")

# Ensure the 'finish' variable is 1 when beets are 0 using indicator constraints

for i in I:
    for t in T:
        beet = (beet_flow[i, 0, 0, t])
        model.addConstr((finish[i, t] == 1) >> (beet <= 1))

# Optimize the model
model.optimize()

# Check and print the results
if model.status == GRB.OPTIMAL:
    for i in I:
        for t in T:
            print(f"finish[{i},{t}] = {finish[i, t].x}")
            print(f"Beets [{i}, {t}]: {beet_flow[i,0,0,t]}")

 

Output:

 

Traceback (most recent call last):
  File "/Users/...", line 36, in <module>
    model.addConstr((finish[i, t] == 1) >> (beet <= 1))
  File "src/gurobipy/model.pxi", line 3637, in gurobipy.Model.addConstr
  File "src/gurobipy/model.pxi", line 4714, in gurobipy.Model.addGenConstrIndicator
TypeError: unsupported operand type(s) for -=: 'NoneType' and 'float'

0

• 

  Matthias Miltenberger

  Gurobi Staff

  • May 29, 2024 14:07

  Hi Ludwig,

  it seems that "beet" is not a variable, so you also cannot use it to construct the constraint "beet <= 1". You may have to add another call to addVariable() to do something with those beet values.

  I hope that helps.

  Cheers,
  Matthias

   

  1
• 

  Ludwig Baunach

  • May 29, 2024 14:30

  

  

  Thank you that solved the problem

  0

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