AMPL GURUBI bestbound

Answered

hector garcia

• April 02, 2020 18:15

While solving mixed integer lineal models using gurobi in ampl , the bestbound reported is always 0, eaen when reaching the time limit and getting just a feasible solution, what am i doing wrong?

below the instructions used in ampl and the results display, Z is my objective function.

ampl: reset;
ampl: model ModeloMaster.mod;
ampl: option solver gurobi;
ampl: option gurobi_options 'timing 1' 'timelim=60' 'bestbound=1';

ampl: data m5n50t0.6r0.8-B-6.dat;
ampl: solve;
ampl: display Z , Z.bestbound, Z.relax, _solve_elapsed_time , solve_result ;

 

Gurobi 9.0.0: timing 1
timelim=100
bestbound=1

Times (seconds):
Input = 0.078125
Solve = 392.234 (summed over threads)
Output = 0.015625
Elapsed = 101
Gurobi 9.0.0: time limit with a feasible solution; objective 206
842838 simplex iterations
1843 branch-and-cut nodes
absmipgap = 206, relmipgap = 1
No basis.
No dual variables returned.

suffix bestbound OUT;
Z = 206
Z.bestbound = 0
Z.relax = 0
_solve_time = 392.344
_solve_elapsed_time = 101.344
solve_result = limit

0

• 

  Eli Towle

  Gurobi Staff

  • April 03, 2020 23:24

  Hi Hector,

  Are you able to look at the full log produced by Gurobi? It seems that Gurobi does not improve the objective bound past \( 0 \) in the 60-second time limit. If you want to focus on improving the bound, a good place to start is to set the Cuts parameter to a more aggressive value and/or the MIPFocus parameter to 3. Of course, if the optimal objective value is \( 0 \), then the bound cannot be improved any further.

  Thanks,

  Eli

  0
• 

  Pritom Kumar Mondal

  • August 27, 2021 18:57
  • Edited

  

  

  Hello,

  I am having a similar problem. I am trying to find out the best bound of a simple test problem so that I can use it in my original problem. I am using the following commands on AMPL.

  model 2Modefile.mod;
  data 2dataset.dat;
  option gurobi_options 'bestbound=1';
  option solver gurobi;

  solve;

  The output is the following.

  Gurobi 9.1.1: bestbound=1
  Gurobi 9.1.1: optimal solution; objective 13150
  4 simplex iterations

  suffix bestbound OUT;

  My question is why it is showing "bestbound OUT"?

  Thanks,

  Pritom

  0
• 

  Robert Fourer

  • August 27, 2021 21:01

  

  

  I answered this question in another thread where you asked it today.

  0

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