Error in Lazy constraints aith summation

Hamid Nazari

2020年04月09日 01:56

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I am trying to add lazy constraints in my callback function in python. The constraint is actually a set of  constraints that each of them has a summation in their expressions. But I am getting this error:

TypeError: unsupported operand type(s) for -: 'generator' and 'NoneType'

 

My call back function is

def cut_callback(model, where):
    if where == GRB.callback.MIPNODE:
        x_temp = model._vars[0:m*n]
        x_temp = np.reshape(x_temp,(m,n))
        y_temp = model._vars[m*n:m*n+n]
        p_temp = model._vars[m*n+n:]
        
        model.cbLazy(gp.quicksum(max([(pL[j] - A[k, j]), (pL[i] - A[k, i])])
                                 *x_temp[k-1,i-1] for i in J) + (A[k, j] - pL[j])
                     *y_temp[j] - p_temp[j] <= -pL[j] for j in J for k in I)

        model.terminate()

I also changed the max in quicksum to gp.max_ but I got the same error. Can you help me figure out what the problem is?

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  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:15 編集済み

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