title: presolved in MILP
body: <p>Presolve: All rows and columns removed
  Iteration    Objective       Primal Inf.    Dual Inf.      Time
         0    9.9086144e-01   0.000000e+00   0.000000e+00      0s
        16    9.9086144e-01   0.000000e+00   0.000000e+00      0s</p>
  
  <p>Solved in 16 iterations and 0.00 seconds
  Optimal objective  9.908614362e-01
  Gurobi 5.5.0: optimal solution; objective 0.9908614362
  16 simplex iterations</p>
  
  <p>whats the problem and I cannt find it for two weeks. I can test the model right under small network data file. But when I test under larger network with more nodes, it occurs this kind of problems shown above.</p>