TypeError: must be real number, not Var

[StevenQiu1]

My objective function is this

\mbox{Average Profit under }(s_1,s_2,...,s5)=\max \quad & \frac{1}{5}\sum{k=1}^5 \left(\sum{i=1}^m\sum{j=1}^n (12.25-c{ij})x{ij}^k\right)\

Here's what I wrote model.setObjective(quicksum((r-c[i,j]) * math.pow(x[i,j,k] ,k)for i in range(n) for j in range(m) for k in range(5)), GRB.MAXIMIZE)

Errors

-TypeError: must be real number, not Var

[mattmilten]

Hi Steven,

You cannot put the exponent directly into the objective. You need to add an auxiliary variable to hold that value and then put this into the objective:

xpow = model.addVars(n,m,5)
for k in range(5):
    for i in range(n):
        for j in range(m):
            model.addGenConstrPow(x[i,j,k], xpow[i,j,k], k)
model.setObjective(quicksum((r-c[i,j]) * xpow[i,j,k] for i in range(n) for j in range(m) for k in range(5)), GRB.MAXIMIZE)

You can read more about this constraint type here: Model.addGenConstrPow