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

• Official comment

  

  Simranjit Kaur

  Gurobi Staff

  • December 06, 2024 00:47

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum. Or why not try our AI Gurobot?.
• 

  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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