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Getting to know which cuts are applied at root node

  • 1.  Getting to know which cuts are applied at root node

    Posted 10/07/12 10:06 PM

    Originally posted by: Marc-AndreCarle


    Hi,

    I used interactive CPLEX to find the optimal to a given model. At root nodes, CPLEX indicates that it performs cuts, by lines such as these:

    Problem 'U:\Benchmark\MIPLIB2010\enlight13.mps' read.
    Read time = 0.02 sec.
    Tried aggregator 1 time.
    Reduced MIP has 169 rows, 338 columns, and 962 nonzeros.
    Reduced MIP has 172 binaries, 166 generals, 0 SOSs, and 0 indicators.
    Probing time = 0.00 sec.
    Tried aggregator 1 time.
    Presolve time = 0.02 sec.
    Probing time = 0.00 sec.
    Clique table members: 9.
    MIP emphasis: balance optimality and feasibility.
    MIP search method: dynamic search.
    Parallel mode: deterministic, using up to 4 threads.
    Root relaxation solution time = 0.00 sec.

    Nodes Cuts/
    Node Left Objective IInf Best Integer Best Bound ItCnt Gap

    0 0 1.0000 2 1.0000 0
    0 0 1.5000 10 Cuts: 6 55
    0 0 2.5000 8 Cuts: 19 59
    0 0 3.0000 14 Cuts: 19 64
    0 0 3.0000 22 Cuts: 27 73
    0 0 3.2941 27 Cuts: 25 87
    0 0 3.4859 31 Cuts: 24 94
    0 0 3.7967 38 Cuts: 22 104
    http://...
    And so on... but when I get the optimal solution, the log says no cuts have been applied:

    Elapsed real time = 8.07 sec. (tree size = 0.57 MB, solutions = 0)
    • 36333 9250 integral 0 71.0000 20.3333 287587 71.36%

    GUB cover cuts applied: 0
    Clique cuts applied: 0
    Cover cuts applied: 0
    Implied bound cuts applied: 0
    Flow cuts applied: 0
    Mixed integer rounding cuts applied: 0
    Flow path cuts applied: 0
    Zero-half cuts applied: 0
    Multi commodity flow cuts applied: 0
    Gomory fractional cuts applied: 0
    Disjunctive cuts applied: 0

    How can I know which cuts have been applied by reading the log?

    Thanks,
    Marc-Andre
    #CPLEXOptimizers
    #DecisionOptimization


  • 2.  Re: Getting to know which cuts are applied at root node

    Posted 10/12/12 10:40 AM

    Originally posted by: SystemAdmin


    Hi Marc-Andre,

    the cuts that you see in the log files have indeed been added to the LP relaxation.
    But since CPLEX can purge cuts again lateron, you can still end up with zero cuts.
    Note that the cut statistics at the end only list those cuts that are in the LP relaxation at the very end of the optimization. It does not give any indication on what cuts were active during the search.

    Thus, if you see at the end that 0 cuts were in use, it does not mean that you can turn off all cut separators and still get the same solving behavior.
    Tobias
    #CPLEXOptimizers
    #DecisionOptimization


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