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I'm having difficulties understanding my FlowControl output compared to what the Engine Log shows me.

Scripting Log (left) and Engine Log (right)

My output from the FlowControl into the Scripting Log (yellow marks) is cplex.getObjValue(), then cplex.getBestObjValue(), and cplex.getMIPRelativeGap(). The Engine log shows the last entry before the optimization is terminated. I have a dettillim = 15000, which doesn't seem to be reached, but also a few fixed binary variables (LB==UB), so I'm expecting a gap.

Now my question is why (and/or how) does the MIP gap extracted from the FlowControl differ from the last entry in the Engine Log? I can't find any reasonable explanation in the documentation.

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    $\begingroup$ Is it possible that the engine log does not print every single line ? $\endgroup$
    – Kuifje
    Commented Oct 22, 2020 at 12:18

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The engine log does not print the gap for every node cplex investigates. That would leave you with more than 2000 lines in the log for your instance. So cplex has done some work between the last line in the engine log and the time it terminates.

I must admit I do not know anything about the frequency with which cplex outputs a line in the engine log. It might be node or time specific?

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    $\begingroup$ By default the output is node specific, plus a line for each integer feasible solution. It is configurable with the MIPInterval parameter. Additionally the MIPDisplay parameter must be greater than 1 in order for node logs to appear. $\endgroup$
    – Michael Chan
    Commented Oct 22, 2020 at 17:14
  • $\begingroup$ @MichaelChan Thanks, very useful, I didn't know $\endgroup$
    – Sune
    Commented Oct 22, 2020 at 17:39
  • $\begingroup$ Thank you both! Too bad it doesn't at least print the final values automatically when the solver terminates before reaching optimality... $\endgroup$
    – Frédéric Jung-Plan
    Commented Oct 22, 2020 at 18:19

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