Yuriy Zinchenko

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Latest activity by Yuriy Zinchenko

  • Yuriy Zinchenko commented,

    1. Community
    2. Modeling
    3. Minimal constraints needed to prove the contradiction

    Thank you for the feedback, Saska.  One thing I could potentially add is that right now we deliver a small IIS with high probability, due to the nature of how things are implemented. That is, if yo...

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  • Yuriy Zinchenko commented,

    1. Community
    2. Algorithms
    3. Crossover impact on duals in a LP

    ps: with respect how the crossover comes into play, if the model is degenerate, the algorithmic path alone will determine the values here. From a user point of view this may seem like the outcome d...

  • Yuriy Zinchenko commented,

    Official comment
    1. Community
    2. Algorithms
    3. Crossover impact on duals in a LP

    Hi Elena, to chirp in here, most likely your dual is what is called degenerate, that is, admits several solutions, in which case you may see some surpassing values coming up as well as should proba...

  • Yuriy Zinchenko commented,

    Official comment
    1. Community
    2. Algorithms
    3. Checking feasibility of the problem

    Hello again, Andrey. Thank you again for asking an interesting Q.  The problem instance you have shared is small, but is seemingly tough to determine feasibility.  Our apologies for not replying so...

  • Yuriy Zinchenko commented,

    1. Community
    2. Algorithms
    3. How Gurobi compute IIS for MIP problem?

    Great to hear this is helpful. Stay well, Ramy, and please say "hello" to John if you run into him; he may remember Yuriy who was a PDF at McMaster when Professor Chinneck visited. Regards.

  • Yuriy Zinchenko commented,

    1. Community
    2. Algorithms
    3. How Gurobi compute IIS for MIP problem?

    > If Guroubi computes IIS using a filtering algorithm, that means we can attempt to get multiple IISes by shuffling the constraints in the model, correct? I tried doing that but Guroubi's computIIS...

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    • 1 vote

  • Yuriy Zinchenko commented,

    Official comment
    1. Community
    2. Algorithms
    3. How Gurobi compute IIS for MIP problem?

    Hello Ramy, Thanks for asking! :) 1. For LP, computing all III's based on the dual, as you said, is equivalent to enumerating all the vertices of the respective dual polyhedron, which could be a ma...

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  • Yuriy Zinchenko commented,

    Official comment
    1. Community
    2. Algorithms
    3. Determine the solution from the optimal facet in LP

    Hello Taejoon, 1) for a polytope {x: Ax <= b} the analytic centre x* is computed as a minimizer of the log-barrier,  x* = arg min { -\sum_i (b - Ax)_i : Ax <= b } Now, if LP has multiple solutions,...

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  • Yuriy Zinchenko commented,

    Official comment
    1. Community
    2. Algorithms
    3. Does the barrier method for LP automatically start from the dual problem?

    Hello Bo:   we do apply dual transformation automatically (in some cases), specifically, indeed, when A is "long and narrow" we would look into that with the code. In other words, the matrix "aspec...

  • Yuriy Zinchenko commented,

    1. Community
    2. Algorithms
    3. Theoretical Background on BarHomogeneous parameter

    Hello Yannic: barHomogeneous = 1 parameter refers to using the so-called homogeneous self-dual embedding that amongst other things allows to set the initial point for the barrier (the other alterna...