Presolve: All rows and columns removed

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7046...@qq.com

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May 31, 2016, 11:46:19 PM5/31/16
to Gurobi Optimization
Here is the running result. I can't get a result or I have get the result. Because I test my model under small network, we can get perfect answer, in which sum_flow1 and sum_flow2 had values not 0. However, when I test the model under larger network, I just get the answer as bellow, in which the sum_flow1 and sum_flow2 always had value 0.
Besides, why does it accur--Presolve: All rows and columns removed?
Because it doesn't appear when I test a small network, but in larger networks.


Gurobi 5.5.0: mipgap = 0.000000000000000000000000000000000000000000000000000000001
outlev = 1
Optimize a model with 2050 rows, 270 columns and 1534 nonzeros
Presolve removed 270 rows and 2050 columns
Presolve time: 0.00s
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

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
sum_flow1 [*,*] (tr)
:     P2  P4  P5    :=
P2N1   0   .   .
P2N2   0   .   .
P2N3   0   .   .
P2N4   0   .   .
P2N5   0   .   .
P2N6   0   .   .
P2N7   0   .   .
P2N8   0   .   .
P2N9   0   .   .
P4N1   .   0   .
P4N2   .   0   .
P4N3   .   0   .
P4N4   .   0   .
P4N5   .   0   .
P4N6   .   0   .
P4N7   .   0   .
P4N8   .   0   .
P5N1   .   .   0
P5N2   .   .   0
P5N3   .   .   0
P5N4   .   .   0
P5N5   .   .   0
P5N6   .   .   0
P5N7   .   .   0
P5N8   .   .   0
P5N9   .   .   0
;

sum_flow2 [*,*] (tr)
:     P2  P4  P5    :=
P2N1   0   .   .
P2N2   0   .   .
P2N3   0   .   .
P2N4   0   .   .
P2N5   0   .   .
P2N6   0   .   .
P2N7   0   .   .
P2N8   0   .   .
P2N9   0   .   .
P4N1   .   0   .
P4N2   .   0   .
P4N3   .   0   .
P4N4   .   0   .
P4N5   .   0   .
P4N6   .   0   .
P4N7   .   0   .
P4N8   .   0   .
P5N1   .   .   0
P5N2   .   .   0
P5N3   .   .   0
P5N4   .   .   0
P5N5   .   .   0
P5N6   .   .   0
P5N7   .   .   0
P5N8   .   .   0
P5N9   .   .   0
;


I need help from all of you .
Thank you.
my email address is: hch...@foxmail.com

Tobias Achterberg

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Jun 1, 2016, 4:36:31 AM6/1/16
to gur...@googlegroups.com
It just seems that for this particular problem instance the zero solution is
feasible. My guess is that there is nothing in the model that would trigger
activity. For example, it could be that there is no demand that needs to be
satisfied.

Tobias
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