How to get the index value of binary variable using indicator constraint

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Namkyoung Lee

2022年02月21日 00:23

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This thread resumes Indicator constraint which contains constant value.

I adopted indicator constraint previously you recommended and focused on programming which means that constant A equals constant B, in the right side of indicator constraint operator, >>.
In the following sample code, I used t to get the value of index i of b[i]. And z consisting of t becomes input for the formulation included in objective function. 
For instance, if b[1], b[3] and b[5] ==1, then t=1, 3, 5. However this part brought the error, TypeError: unsupported operand type(s) for -=: 'NoneType' and 'float'. At this point, I have no idea how to fix it. If the error is solved, z will become [1,3,5]. And z is entered as parameter of tmp_f(), a part of objective.

# Rest of model

def tmp_f(z):
    k = np.array([1 for i in range(10)])
    for j in z:
        k[j] = 0
    return sum((k+1)**2)

# Indicator constraints
z = []     # ← ← Initialization of an input for nonlinear-type formulation
t = -1
for i in range(10):
    m.addConstr((b[i] == 1) >> (t == i))
    z.append(t)

# Objective function
obj = gp.quicksum(x[i] + y[i] for i in range(10))
m.setObjective(obj + tmp_f(z), GRB.MAXIMIZE)

# Rest of model

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  Jaromił Najman

  • Gurobi Staff

  2022年02月21日 08:16

  This question has been answered in Indicator constraint which contains constant value.

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